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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenThu, 29 Feb 2024 01:53:18 +0000Spin reduction transition in spin-3/2 random Heisenberg chains
https://resolver.caltech.edu/CaltechAUTHORS:REFprb02
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Kehrein-S', 'name': {'family': 'Kehrein', 'given': 'Stefan'}}, {'id': 'Fisher-D-S', 'name': {'family': 'Fisher', 'given': 'Daniel S.'}}]}
Year: 2002
DOI: 10.1103/PhysRevB.66.060402
Random spin-3/2 antiferromagnetic Heisenberg chains are investigated using an asymptotically exact renormalization group. Randomness is found to induce a quantum phase transition between two random-singlet phases. In the strong randomness phase the effective spins at low energies are Seff=3/2, while in the weak randomness phase the effective spins are Seff=1/2. Separating them is a quantum critical point near which there is a nontrivial mixture of spin-1/2, spin-1, and spin-3/2 effective spins at low temperatures.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nxvjd-f5t31Dissipation and quantum phase transitions of a pair of Josephson junctions
https://resolver.caltech.edu/CaltechAUTHORS:REFprb03
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'Eugene'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Fisher-D-S', 'name': {'family': 'Fisher', 'given': 'Daniel S.'}}]}
Year: 2003
DOI: 10.1103/PhysRevB.68.214515
A model system consisting of a mesoscopic superconducting grain coupled by Josephson junctions to two macroscopic superconducting electrodes is studied. We focus on the effects of Ohmic dissipation caused by resistive shunts and superconducting-normal charge relaxation within the grain. As the temperature is lowered, the behavior crosses over from uncoupled Josephson junctions, similar to situations analyzed previously, to strongly interacting junctions. The crossover temperature is related to the energy-level spacing of the grain and is of the order of the inverse escape time from the grain. In the limit of zero temperature, the two-junction system exhibits five distinct quantum phases, including a novel superconducting state with localized Cooper pairs on the grain but phase coherence between the leads due to Cooper pair cotunneling processes. In contrast to a single junction, the transition from the fully superconducting to fully normal phases is found to be controlled by an intermediate-coupling fixed point whose critical exponents vary continuously as the resistances are changed. The model is analyzed via two-component sine-Gordon models and related Coulomb gases that provide effective low-temperature descriptions in both the weak and strong Josephson coupling limits. The complicated phase diagram is consistent with symmetries of the two component sine-Gordon models, which include weak- to strong-coupling duality and permutation triality. Experimental consequences of the results and potential implications for superconductor to normal transitions in thin wires and films are discussed briefly.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zncw8-psc26Energy correlations in random transverse field Ising spin chains
https://resolver.caltech.edu/CaltechAUTHORS:REFprb04
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Fisher-D-S', 'name': {'family': 'Fisher', 'given': 'Daniel S.'}}]}
Year: 2004
DOI: 10.1103/PhysRevB.70.064409
The end-to-end energy-energy correlations of random transverse field quantum Ising spin chains are computed using a generalization of an asymptotically exact real space renormalization group (RG) previously introduced. Away from the critical point, the average energy-energy correlations decay exponentially with a correlation length that is the same as that of the spin-spin correlations. The typical correlations, however, decay exponentially with a characteristic length, proportional to the square root of the primary correlation length. At the quantum critical point, the average correlations decay subexponentially as [overline C[sub L]]~e–const L1/3, whereas the typical correlations decay faster, as ~e<sup>-Ksqrt(L)</sup>, with K a random variable with a universal distribution. The critical energy-energy correlations behave very similarly to the smallest gap, computed previously; this is explained in terms of the RG flow and the excitation structure of the chain. In order to obtain the energy correlations, an extension of the previously used methods was needed; here, this was carried out via RG transformations that involve a sequence of unitary transformations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ndxq4-xt337Phase Transition in a System of One-Dimensional Bosons with Strong Disorder
https://resolver.caltech.edu/CaltechAUTHORS:ALTprl04
Authors: {'items': [{'id': 'Altman-E', 'name': {'family': 'Altman', 'given': 'Elud'}}, {'id': 'Kafri-Y', 'name': {'family': 'Kafri', 'given': 'Yariv'}}, {'id': 'Polkovnikov-A', 'name': {'family': 'Polkovnikov', 'given': 'Anatoli'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2004
DOI: 10.1103/PhysRevLett.93.150402
We study one-dimensional disordered bosons at large commensurate filling. Using a real space renormalization group approach, we find a new random fixed point which controls a phase transition from a superfluid to an incompressible Mott glass. The transition can be tuned by changing the disorder distribution even with vanishing interactions. We derive the properties of the transition, which suggest that it is in the Kosterlitz-Thouless universality class.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/azgs0-qpn28Entanglement Entropy of Random Quantum Critical Points in One Dimension
https://resolver.caltech.edu/CaltechAUTHORS:REFprl04
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Moore-J-E', 'name': {'family': 'Moore', 'given': 'J. E.'}}]}
Year: 2004
DOI: 10.1103/PhysRevLett.93.260602
For quantum critical spin chains without disorder, it is known that the entanglement of a segment of N>>1 spins with the remainder is logarithmic in N with a prefactor fixed by the central charge of the associated conformal field theory. We show that for a class of strongly random quantum spin chains, the same logarithmic scaling holds for mean entanglement at criticality and defines a critical entropy equivalent to central charge in the pure case. This effective central charge is obtained for Heisenberg, XX, and quantum Ising chains using an analytic real-space renormalization-group approach believed to be asymptotically exact. For these random chains, the effective universal central charge is characteristic of a universality class and is consistent with a c-theorem.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1py5w-a6h24Vortices and Quasiparticles near the Superconductor-Insulator Transition in Thin Films
https://resolver.caltech.edu/CaltechAUTHORS:GALprl05
Authors: {'items': [{'id': 'Galitski-V-M', 'name': {'family': 'Galitski', 'given': 'Victor M.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Fisher-Matthew-P-A', 'name': {'family': 'Fisher', 'given': 'Matthew P. A.'}}, {'id': 'Senthil-T', 'name': {'family': 'Senthil', 'given': 'T.'}}]}
Year: 2005
DOI: 10.1103/PhysRevLett.95.077002
We study the low temperature behavior of an amorphous superconducting film driven normal by a perpendicular magnetic-field (B). For this purpose we introduce a new two-fluid formulation consisting of fermionized field-induced vortices and electrically neutralized Bogoliubov quasiparticles (spinons) interacting via a long-ranged statistical interaction. This approach allows us to access a novel non-Fermi-liquid phase, which naturally interpolates between the low B superconductor and the high B normal metal. We discuss the properties of the resulting "vortex metal" phase.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wvf22-gg979Ground-state degeneracy of correlated insulators with edges
https://resolver.caltech.edu/CaltechAUTHORS:REFprb05
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Lin-H-H', 'name': {'family': 'Lin', 'given': 'Hsiu-Hau'}}]}
Year: 2005
DOI: 10.1103/PhysRevB.72.073109
Using the topological flux insertion procedure, the ground-state degeneracy of an insulator on a periodic lattice with filling factor nu=p/q was found to be at least q-fold. Applying the same argument in a lattice with edges, we show that the degeneracy is modified by the additional edge density nuE associated with the open boundaries. To carry out this generalization we demonstrate how to distinguish between bulk and edge states, and follow how an edge modifies the thermodynamic limit of Oshikawa's original argument. In particular, we also demonstrate that these edge corrections may even make an insulator with integer bulk filling degenerate.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/b8q23-y6705Simulation results for an interacting pair of resistively shunted Josephson junctions
https://resolver.caltech.edu/CaltechAUTHORS:WERjsmte05
Authors: {'items': [{'id': 'Werner-P', 'name': {'family': 'Werner', 'given': 'Philipp'}, 'orcid': '0000-0002-2136-6568'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Troyer-M', 'name': {'family': 'Troyer', 'given': 'Matthias'}}]}
Year: 2005
DOI: 10.1088/1742-5468/2005/12/P12003
Using a new cluster Monte Carlo algorithm, we study the phase diagram and critical properties of an interacting pair of resistively shunted Josephson junctions. This system models tunnelling between two electrodes through a small superconducting grain, and is described by a double sine-Gordon model. In accordance with theoretical predictions, we observe three different phases and crossover effects arising from an intermediate coupling fixed point. On the superconductor-to-metal phase boundary, the observed critical behaviour is within error-bars the same as in a single junction, with identical values of the critical resistance and a correlation function exponent which depends only on the strength of the Josephson coupling. We explain these critical properties on the basis of a renormalization group (RG) calculation. In addition, we propose an alternative new mean-field theory for this transition, which correctly predicts the location of the phase boundary at intermediate Josephson coupling strength.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rspeh-dbs50Universal point contact resistance between thin-film superconductors
https://resolver.caltech.edu/CaltechAUTHORS:HERprb06
Authors: {'items': [{'id': 'Hermele-M', 'name': {'family': 'Hermele', 'given': 'Michael'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Fisher-Matthew-P-A', 'name': {'family': 'Fisher', 'given': 'Matthew P. A.'}}, {'id': 'Goldbart-P-M', 'name': {'family': 'Goldbart', 'given': 'Paul M.'}}]}
Year: 2006
DOI: 10.1103/PhysRevB.73.134504
A system comprising two superconducting thin films connected by a point contact is considered. The contact resistance is calculated as a function of temperature and film geometry, and is found to vanish rapidly with temperature, according to a universal, nearly activated form, becoming strictly zero only at zero temperature. At the lowest temperatures, the activation barrier is set primarily by the superfluid stiffness in the films, and displays only a weak (i.e., logarithmic) temperature dependence. The Josephson effect is thus destroyed, albeit only weakly, as a consequence of the power-law-correlated superconducting fluctuations present in the films below the Berezinskii-Kosterlitz-Thouless transition temperature. The behavior of the resistance is discussed, both in various limiting regimes and as it crosses over between these regimes. Details are presented of a minimal model of the films and the contact, and of the calculation of the resistance. A formulation in terms of quantum phase-slip events is employed, which is natural and effective in the limit of a good contact. However, it is also shown to be effective even when the contact is poor and is, indeed, indispensable, as the system always behaves as if it were in the good-contact limit at low enough temperature. A simple mechanical analogy is introduced to provide some heuristic understanding of the nearly activated temperature dependence of the resistance. Prospects for experimental tests of the predicted behavior are discussed, and numerical estimates relevant to anticipated experimental settings are provided.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qkerg-zct30Measuring entanglement entropies in many-body systems
https://resolver.caltech.edu/CaltechAUTHORS:KLIpra06
Authors: {'items': [{'id': 'Klich-I', 'name': {'family': 'Klich', 'given': 'Israel'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Silva-A', 'name': {'family': 'Silva', 'given': 'Alessandro'}}]}
Year: 2006
DOI: 10.1103/PhysRevA.74.032306
We explore the relation between entanglement entropy of quantum many-body systems and the distribution of corresponding, properly selected, observables. Such a relation is necessary to actually measure the entanglement entropy. We show that, in general, the Shannon entropy of the probability distribution of certain symmetry observables gives a lower bound to the entropy. In some cases this bound is saturated and directly gives the entropy. We also show other cases in which the probability distribution contains enough information to extract the entropy: we show how this is done in several examples including BEC wave functions, the Dicke model, XY spin chain, and chains with strong randomness.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/14krm-scz52Transverse Meissner physics of planar superconductors with columnar pins
https://resolver.caltech.edu/CaltechAUTHORS:REFprb06
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Hofstetter-W', 'name': {'family': 'Hofstetter', 'given': 'Walter'}}, {'id': 'Nelson-D-R', 'name': {'family': 'Nelson', 'given': 'David R.'}}]}
Year: 2006
DOI: 10.1103/PhysRevB.74.174520
The statistical mechanics of thermally excited vortex lines with columnar defects can be mapped onto the physics of interacting quantum particles with quenched random disorder in one less dimension. The destruction of the Bose glass phase in type-II superconductors, when the external magnetic field is tilted sufficiently far from the column direction, is described by a poorly understood non-Hermitian quantum phase transition. We present here exact results for this transition in (1+1) dimensions, obtained by mapping the problem in the hard core limit onto one-dimensional fermions described by a non-Hermitian tight binding model. Both site randomness and the relatively unexplored case of bond randomness are considered. Analysis near the mobility edge and near the band center in the latter case is facilitated by a real space renormalization group procedure used previously for Hermitian quantum problems with quenched randomness in one dimension.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6v71z-w0s45Superconductor-to-normal transitions in dissipative chains of mesoscopic grains and nanowires
https://resolver.caltech.edu/CaltechAUTHORS:REFprb07
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'Eugene'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Fisher-D-S', 'name': {'family': 'Fisher', 'given': 'Daniel S.'}}]}
Year: 2007
DOI: 10.1103/PhysRevB.75.014522
The interplay of quantum fluctuations and dissipation in chains of mesoscopic superconducting grains is analyzed and the results are applied to nanowires. It is shown that in one dimensional arrays of resistively shunted Josephson junctions, the superconducting-normal charge relaxation within the grains plays an important role. At zero temperature, two superconducting phases can exist, depending primarily on the strength of the dissipation. In the fully superconducting phase (FSC), each grain acts superconducting, and the coupling to the dissipative conduction is important. In the SC[small star, filled] phase, the dissipation is irrelevant at long wavelengths. The transition between these two phases is driven by quantum phase slip dipoles, and is primarily local, with continuously varying critical exponents. In contrast, the transition from the SC[small star, filled] phase to the normal metallic phase is a Kosterlitz-Thouless transition with global character (i.e., determined by the field behavior at large wavelengths). Most interesting is the transition from the FSC phase directly to the normal phase: this transition, which has mixed local and global characteristics, can be one of three distinct types. The corresponding segments of the phase boundary come together at bicritical points. The zero-temperature phase diagram, as well as the finite-temperature scaling behavior are inferred from both weak and strong coupling renormalization group analyses. At intermediate temperatures, near either superconductor-to-normal phase transition, there are regimes of super-metallic behavior, in which the resistivity first decreases gradually with decreasing temperature before eventually increasing as temperature is lowered further. The results on chains of Josephson junctions are extended to continuous superconducting nanowires and the subtle issue of whether these can exhibit an FSC phase is considered. Potential relevance to superconductor-metal transitions in other systems is also discussed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dzq5w-bd547Sharp Superconductor-Insulator Transition in Short Wires
https://resolver.caltech.edu/CaltechAUTHORS:MEIprl07
Authors: {'items': [{'id': 'Meidan-D', 'name': {'family': 'Meidan', 'given': 'Dganit'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2007
DOI: 10.1103/PhysRevLett.98.187001
Recent experiments on short MoGe nanowires show a sharp superconducting-insulating transition at the universal resistance RQ=h/(4e^2), contrary to the expectation of a smooth temperature dependence of the resistance for such Josephson-like systems. We present a self-consistent renormalization-group treatment of interacting quantum phase slips in short superconducting wires, which reproduces this sharp universal transition. Our method should also apply to other systems in the sine-Gordon universality class, in the previously inaccessible intermediate-coupling regime.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vt8hw-cnc38Sagnac Interference in Carbon Nanotube Loops
https://resolver.caltech.edu/CaltechAUTHORS:REFprl07b
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Heo-J', 'name': {'family': 'Heo', 'given': 'Jinseong'}}, {'id': 'Bockrath-M-W', 'name': {'family': 'Bockrath', 'given': 'Marc'}}]}
Year: 2007
DOI: 10.1103/PhysRevLett.98.246803
In this Letter we study electron interference in nanotube loops. The conductance as a function of the applied voltage is shown to oscillate due to interference between electron beams traversing the loop in two opposite directions, with slightly different velocities. The period of these oscillations with respect to the gate voltage, as well as the temperatures required for the effect to appear, are shown to be much larger than those of the related Fabry-Perot interference. We calculate interaction effects on the period of the oscillations, and show that even though interactions destroy much of the near degeneracy of velocities in the symmetric spin channel, the slow interference effects survive.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/x1r3k-64t56Entanglement entropy of the random s=1 Heisenberg chain
https://resolver.caltech.edu/CaltechAUTHORS:REFprb07c
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Moore-J-E', 'name': {'family': 'Moore', 'given': 'J. E.'}}]}
Year: 2007
DOI: 10.1103/PhysRevB.76.024419
Random spin chains at quantum critical points exhibit an entanglement entropy between a segment of length L and the rest of the chain that scales as log2 L with a universal coefficient. Since for pure quantum critical spin chains this coefficient is fixed by the central charge of the associated conformal field theory, the universal coefficient in the random case can be understood as an effective central charge. In this paper we calculate the entanglement entropy and effective central charge of the spin-1 random Heisenberg model in its random-singlet phase and also at the critical point at which the Haldane phase breaks down. The latter is the first entanglement calculation for an infinite-randomness fixed point that is not in the random-singlet universality class. Our results are consistent with a c-theorem for flow between infinite-randomness fixed points. The formalism we use can be generally applied to calculation of quantities that depend on the RG history in s>=1 random Heisenberg chains.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y7bpy-fss78Superfluidity and Magnetism in Multicomponent Ultracold Fermions
https://resolver.caltech.edu/CaltechAUTHORS:CHEprl07
Authors: {'items': [{'id': 'Cherng-R-W', 'name': {'family': 'Cherng', 'given': 'R. W.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'E.'}}]}
Year: 2007
DOI: 10.1103/PhysRevLett.99.130406
We study the interplay between superfluidity and magnetism in a multicomponent gas of ultracold fermions. Ward-Takahashi identities constrain possible mean-field states describing order parameters for both pairing and magnetization. The structure of global phase diagrams arises from competition among these states as functions of anisotropies in chemical potential, density, or interactions. They exhibit first and second order phase transition as well as multicritical points, metastability regions, and phase separation. We comment on experimental signatures in ultracold atoms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gyt2t-k8y94Universal Periods in Quantum Hall Droplets
https://resolver.caltech.edu/CaltechAUTHORS:FIEprl07
Authors: {'items': [{'id': 'Fiete-G-A', 'name': {'family': 'Fiete', 'given': 'Gregory A.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Fisher-Matthew-P-A', 'name': {'family': 'Fisher', 'given': 'Matthew P. A.'}}]}
Year: 2007
DOI: 10.1103/PhysRevLett.99.166805
Using the hierarchy picture of the fractional quantum Hall effect, we study the ground-state periodicity of a finite size quantum Hall droplet in a quantum Hall fluid of a different filling factor. The droplet edge charge is periodically modulated with flux through the droplet and will lead to a periodic variation in the conductance of a nearby point contact, such as occurs in some quantum Hall interferometers. Our model is consistent with experiment and predicts that superperiods can be observed in geometries where no interfering trajectories occur. The model may also provide an experimentally feasible method of detecting elusive neutral modes and otherwise obtaining information about the microscopic edge structure in fractional quantum Hall states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s6hv2-4yj60Supercurrent Survival under a Rosen-Zener Quench of Hard-Core Bosons
https://resolver.caltech.edu/CaltechAUTHORS:KLIprl07
Authors: {'items': [{'id': 'Klich-I', 'name': {'family': 'Klich', 'given': 'I.'}}, {'id': 'Lannert-C', 'name': {'family': 'Lannert', 'given': 'C.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}]}
Year: 2007
DOI: 10.1103/PhysRevLett.99.205303
We study the survival of supercurrents in a system of impenetrable bosons on a lattice, subject to a quantum quench from its critical superfluid phase to an insulating phase. We show that the evolution of the current when the quench follows a Rosen-Zener profile is exactly solvable. This allows us to analyze a quench of arbitrary rate, from a sudden destruction of the superfluid to a slow opening of a gap. The decay and oscillations of the current are analytically derived and studied numerically along with the momentum distribution after the quench. In the case of small supercurrent boosts nu, we find that the current surviving at long times is proportional to nu^3.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2fcss-f5f91Sharp superconductor–insulator transition in short wires
https://resolver.caltech.edu/CaltechAUTHORS:20100722-100915751
Authors: {'items': [{'id': 'Meidan-D', 'name': {'family': 'Meidan', 'given': 'Dganit'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Smith-R-A', 'name': {'family': 'Smith', 'given': 'Robert A.'}}]}
Year: 2008
DOI: 10.1016/j.physc.2007.09.019
Recent experiments on short MoGe nanowires show a sharp superconductor–insulator transition tuned by the normal state resistance of the wire, with a critical resistance of R_c ≈ R_Q = h/(4e^2). These results are at odds with a broad range of theoretical work on Josephson-like systems that predicts a smooth transition, tuned by the value of the resistance that shunts the junction. We develop a self-consistent renormalization group treatment of interacting phase-slips and their dual counterparts, correlated cooper pair tunneling, beyond the dilute approximation. This analysis leads to a very sharp transition with a critical resistance of R_Q. The addition of the quasi-particles' resistance at finite temperature leads to a quantitative agreement with the experimental results. This self-consistent renormalization group method should also be applicable to other physical systems that can be mapped onto similar sine-Gordon models, in the previously inaccessible intermediate-coupling regime.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/x4dsx-a3s64Sharp Superconductor-Insulator Transition in Short Wires
https://resolver.caltech.edu/CaltechAUTHORS:20091016-111619225
Authors: {'items': [{'id': 'Meidan-D', 'name': {'family': 'Meidan', 'given': 'Dganit'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Smith-R-A', 'name': {'family': 'Smith', 'given': 'Robert A.'}}]}
Year: 2008
DOI: 10.1016/j.physc.2007.09.019
Recent experiments on short MoGe nanowires show a sharp superconductor–insulator transition tuned by the normal state resistance of the wire, with a critical resistance of R_c ≈ R_Q = h/(4e^2). These results are at odds with a broad range of theoretical work on Josephson-like systems that predicts a smooth transition, tuned by the value of the resistance that shunts the junction. We develop a self-consistent renormalization group treatment of interacting phase-slips and their dual counterparts, correlated cooper pair tunneling, beyond the dilute approximation. This analysis leads to a very sharp transition with a critical resistance of R_Q. The addition of the quasi-particles' resistance at finite temperature leads to a quantitative agreement with the experimental results. This self-consistent renormalization group method should also be applicable to other physical systems that can be mapped onto similar sine-Gordon models, in the previously inaccessible intermediate-coupling regime.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2s378-baz28Superfluid-insulator transition in Fermi-Bose mixtures and the orthogonality catastrophe
https://resolver.caltech.edu/CaltechAUTHORS:REFprb08
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'E.'}}]}
Year: 2008
DOI: 10.1103/PhysRevB.77.144511
The superfluid-insulator transition of bosons is strongly modified by the presence of fermions. Through an imaginary-time path-integral approach, we derive the self-consistent mean-field transition line, and account for both the static and dynamic screening effects of the fermions. We find that an effect akin to the fermionic orthogonality catastrophe, arising from the fermionic screening fluctuations, suppresses superfluidity. We analyze this effect for various mixture parameters and temperatures, and consider possible signatures of the orthogonality-catastrophe effect in other measurables of the mixture.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vxcd5-7cf66Effect of inhomogeneous coupling on BCS superconductors
https://resolver.caltech.edu/CaltechAUTHORS:ZOUprb08
Authors: {'items': [{'id': 'Zou-Y', 'name': {'family': 'Zou', 'given': 'Yue'}}, {'id': 'Klich-I', 'name': {'family': 'Klich', 'given': 'Israel'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2008
DOI: 10.1103/PhysRevB.77.144523
We investigate the influence of inhomogeneity in the pairing coupling constant U(r-vector) on dirty BCS superconductors, focusing on Tc, the order parameter Delta(r-vector), and the energy gap Eg(r-vector). Within mean-field theory, we find that when the length scale of the inhomogeneity is comparable to or larger than the coherence length, the ratio 2Eg/Tc is significantly reduced from that of a homogeneous superconductor, while in the opposite limit, this ratio stays unmodified. In two dimensions, when strong phase fluctuations are included, the Kosterlitz-Thouless temperature TKT is also studied. We find that when the inhomogeneity length scale is much larger than the coherence length, 2Eg/TKT can be larger than the usual BCS value. We use our results to qualitatively explain recent experimental observation of a surprisingly low value of 2Eg/Tc in thin films.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wv3m1-wgd98Vortex lattice locking in rotating two-component Bose–Einstein condensates
https://resolver.caltech.edu/CaltechAUTHORS:BARnjp08
Authors: {'items': [{'id': 'Barnett-R', 'name': {'family': 'Barnett', 'given': 'Ryan'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Porter-M-A', 'name': {'family': 'Porter', 'given': 'Mason A.'}}, {'id': 'Büchler-H-P', 'name': {'family': 'Büchler', 'given': 'Hans Peter'}}]}
Year: 2008
DOI: 10.1088/1367-2630/10/4/043030
The vortex density of a rotating superfluid, divided by its particle mass, dictates the superfluid's angular velocity through the Feynman relation. To find how the Feynman relation applies to superfluid mixtures, we investigate a rotating two-component Bose–Einstein condensate, composed of bosons with different masses. We find that in the case of sufficiently strong interspecies attraction, the vortex lattices of the two condensates lock and rotate at the drive frequency, while the superfluids themselves rotate at two different velocities, whose ratio equals the ratio between the particle masses of the two species. In this paper, we characterize the vortex-locked state, establish its regime of stability, and find that it survives within a disk smaller than a critical radius, beyond which vortices become unbound and the two Bose-gas rings rotate together at the frequency of the external drive.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2a3s3-jtn25Insulating Phases and Superfluid-Insulator Transition of Disordered Boson Chains
https://resolver.caltech.edu/CaltechAUTHORS:ALTprl08
Authors: {'items': [{'id': 'Altman-E', 'name': {'family': 'Altman', 'given': 'Ehud'}}, {'id': 'Kafri-Y', 'name': {'family': 'Kafri', 'given': 'Yariv'}}, {'id': 'Polkovnikov-A', 'name': {'family': 'Polkovnikov', 'given': 'Anatoli'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2008
DOI: 10.1103/PhysRevLett.100.170402
Using a strong disorder real-space renormalization group, we study the phase diagram of a fully disordered chain of interacting bosons. Since this approach does not suffer from runaway flows, it allows a direct study of the insulating phases, not accessible in a weak disorder perturbative treatment. We find that the universal properties of the insulating phase are determined by the details and symmetries of the on-site chemical-potential disorder. Three insulating phases are possible: (i) an incompressible Mott glass with a finite superfluid susceptibility, (ii) a random-singlet glass with diverging compressibility and superfluid susceptibility, (iii) a Bose glass with a finite compressibility but diverging superfluid susceptibility. In addition to characterizing the insulating phases, we show that the superfluid-insulator transition is always described by Kosterlitz-Thouless-like flows.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1dh1n-yve37Dissipation-Driven Quantum Phase Transition in Superconductor-Graphene Systems
https://resolver.caltech.edu/CaltechAUTHORS:LUTprl08
Authors: {'items': [{'id': 'Lutchyn-R-M', 'name': {'family': 'Lutchyn', 'given': 'Roman M.'}, 'orcid': '0000-0002-0222-9728'}, {'id': 'Galitski-V-M', 'name': {'family': 'Galitski', 'given': 'Victor M.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Das-Sarma-S', 'name': {'family': 'Das Sarma', 'given': 'S.'}}]}
Year: 2008
DOI: 10.1103/PhysRevLett.101.106402
We show that a system of Josephson junctions coupled via low-resistance tunneling contacts to graphene substrate(s) may effectively operate as a current switching device. The effect is based on the dissipation-driven superconductor-to-insulator quantum phase transition, which happens due to the interplay of the Josephson effect and Coulomb blockade. Coupling to a graphene substrate with gapless excitations further enhances charge fluctuations favoring superconductivity. The effect is shown to scale exponentially with the Fermi energy in graphene, which can be controlled by the gate voltage. We develop a theory that quantitatively describes the quantum phase transition in a two-dimensional Josephson junction array, but it is expected to provide a reliable qualitative description for one-dimensional systems as well.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/41167-bqg55Sagnac interference in carbon nanotubes
https://resolver.caltech.edu/CaltechAUTHORS:BISprb08c
Authors: {'items': [{'id': 'Bishara-W', 'name': {'family': 'Bishara', 'given': 'Waheb'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Bockrath-M-W', 'name': {'family': 'Bockrath', 'given': 'Marc'}}]}
Year: 2008
DOI: 10.1103/PhysRevB.78.165405
The Sagnac interference mode arises when two interfering counterpropogating beams traverse a loop, but with their velocities detuned by a small amount 2u, with vR/L=vF±u. In this paper we perform a perturbative nonequilibrium calculation of Sagnac interference in single-channel wires as well as armchair nanotube loops. We study the dependence of the Sagnac conductance oscillations on temperature and interactions. We find that the Sagnac interference is not destroyed by strong interactions, but becomes weakly dependent on the velocity detuning u. In armchairs nanotubes with typical interaction strength, 0.25<=g<=0.5, we find that the necessary temperature for observing the interference effect, TSAG is also only weakly dependent on the interaction, and is enhanced by a factor of 8 relative to the temperature necessary for observing Fabry-Pérot interference in the same system, TFP.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6q6c4-kgz41Excitations of One-Dimensional Bose-Einstein Condensates in a Random Potential
https://resolver.caltech.edu/CaltechAUTHORS:GURprl08
Authors: {'items': [{'id': 'Gurarie-V', 'name': {'family': 'Gurarie', 'given': 'V.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Chalker-J-T', 'name': {'family': 'Chalker', 'given': 'J. T.'}}]}
Year: 2008
DOI: 10.1103/PhysRevLett.101.170407
We examine bosons hopping on a one-dimensional lattice in the presence of a random potential at zero temperature. Bogoliubov excitations of the Bose-Einstein condensate formed under such conditions are localized, with the localization length diverging at low frequency as [script-l](omega)~1/omegaalpha. We show that the well-known result alpha=2 applies only for sufficiently weak random potential. As the random potential is increased beyond a certain strength, alpha starts decreasing. At a critical strength of the potential, when the system of bosons is at the transition from a superfluid to an insulator, alpha=1. This result is relevant for understanding the behavior of the atomic Bose-Einstein condensates in the presence of random potential, and of the disordered Josephson junction arrays.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xdg9q-d2e59c-theorem violation for effective central charge of infinite-randomness fixed points
https://resolver.caltech.edu/CaltechAUTHORS:FIDprb08
Authors: {'items': [{'id': 'Fidkowski-L', 'name': {'family': 'Fidkowski', 'given': 'L.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Bonesteel-N-E', 'name': {'family': 'Bonesteel', 'given': 'N. E.'}}, {'id': 'Moore-J-E', 'name': {'family': 'Moore', 'given': 'J. E.'}}]}
Year: 2008
DOI: 10.1103/PhysRevB.78.224204
Topological insulators supporting non-Abelian anyonic excitations are in the center of attention as candidates for topological quantum computation. In this paper, we analyze the ground-state properties of disordered non-Abelian anyonic chains. The resemblance of fusion rules of non-Abelian anyons and real-space decimation strongly suggests that disordered chains of such anyons generically exhibit infinite-randomness phases. Concentrating on the disordered golden chain model with nearest-neighbor coupling, we show that Fibonacci anyons with the fusion rule tau[direct-product]tau=1[direct-sum]tau exhibit two infinite-randomness phases: a random-singlet phase when all bonds prefer the trivial fusion channel and a mixed phase which occurs whenever a finite density of bonds prefers the tau fusion channel. Real-space renormalization-group (RG) analysis shows that the random-singlet fixed point is unstable to the mixed fixed point. By analyzing the entanglement entropy of the mixed phase, we find its effective central charge and find that it increases along the RG flow from the random-singlet point, thus ruling out a c theorem for the effective central charge.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/t5pbw-qwa22The universal behavior of a disordered system
https://resolver.caltech.edu/CaltechAUTHORS:20090407-100632110
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2009
DOI: 10.1103/Physics.2.1
The Landau theory of phase transitions and the concept
of symmetry breaking provide a unifying description
of even such seemingly different many-body systems
as a paramagnet cooled to the verge of ferromagnetic
order or a metal approaching the superconducting
transition. What happens, however, when these systems
can lose energy to their environment? For example,
in rare-earth compounds called "heavy-fermion"
materials, the f-shell magnetic moments interact with
a sea of mobile electrons [1]. Similarly, near the metalsuperconductor
transition in ultrathin wires, the electrons
pair up in a connected network of small, superconducting
puddles that are surrounded by a bath of
unpaired metallic electrons [2]. The surrounding metal
gives rise to a parallel resistive channel and hence dissipation.
Introducing dissipation into a many-body quantum
mechanical problem presented a theoretical challenge
that was only resolved in the last quarter of the
20th century [3–5].https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/q0kx7-bw237Superconductor to normal-metal transition in finite-length nanowires: phenomenological model
https://resolver.caltech.edu/CaltechAUTHORS:20090702-094821436
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'Eugene'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}]}
Year: 2009
DOI: 10.1103/PhysRevB.79.094524
In this paper we discuss the interplay of quantum fluctuations and dissipation in uniform superconducting nanowires. We consider a phenomenological model with superconducting and normal components and a finite equilibration rate between these two fluids. We find that phase-slip dipoles proliferate in the wire and decouple the two fluids within its bulk. This implies that the normal fluid only couples to the superconductor fluid through the leads at the edges of the wire, and the local dissipation is unimportant. Therefore, while long wires have a superconductor-metal transition tuned by local properties of the superconducting fluid, short wires have a transition when the total resistance is R_(tot)=R_Q=h/4e^2.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/3anek-qfs07Permutation-symmetric critical phases in disordered non-Abelian anyonic chains
https://resolver.caltech.edu/CaltechAUTHORS:20090603-135244215
Authors: {'items': [{'id': 'Fidkowski-L', 'name': {'family': 'Fidkowski', 'given': 'L.'}}, {'id': 'Lin-H-H', 'name': {'family': 'Lin', 'given': 'H.-H.'}}, {'id': 'Titum-P', 'name': {'family': 'Titum', 'given': 'P.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}]}
Year: 2009
DOI: 10.1103/PhysRevB.79.155120
Topological phases supporting non-Abelian anyonic excitations have been proposed as candidates for topological quantum computation. In this paper, we study disordered non-Abelian anyonic chains based on the quantum groups SU(2)_k, a hierarchy that includes the v = 5/2 fractional quantum Hall state and the proposed v = 12/5 Fibonacci state, among others. We find that for odd k these anyonic chains realize infinite-randomness critical phases in the same universality class as the S_k permutation symmetric multicritical points of Damle and Huse [Phys. Rev. Lett. 89, 277203 (2002)]. Indeed, we show that the pertinent subspace of these anyonic chains actually sits inside the Z_k ⊂ S_k symmetric sector of the Damle-Huse model, and this Z_k symmetry stabilizes the phase.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ps887-yxt27Geometrical approach to hydrodynamics and low-energy excitations of spinor condensates
https://resolver.caltech.edu/CaltechAUTHORS:20090817-144813522
Authors: {'items': [{'id': 'Barnett-R', 'name': {'family': 'Barnett', 'given': 'Ryan'}}, {'id': 'Podolsky-D', 'name': {'family': 'Podolsky', 'given': 'Daniel'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2009
DOI: 10.1103/PhysRevB.80.024420
In this work, we derive the equations of motion governing the dynamics of spin-F spinor condensates. We pursue a description based on standard physical variables (total density and superfluid velocity), alongside 2F "spin nodes:" unit vectors that describe the spin-F state and also exhibit the point-group symmetry of a spinor condensate's mean-field ground state. In the first part of our analysis, we derive the hydrodynamic equations of motion, which consist of a mass continuity equation, 2F Landau-Lifshitz equations for the spin nodes, and a modified Euler equation. In particular, we provide a generalization of the Mermin-Ho relation to spin one and find an analytic solution for the skyrmion texture in the incompressible regime of a spin-half condensate. In the second part, we study the linearized dynamics of spinor condensates. We provide a general method to linearize the equations of motion based on the symmetry of the mean-field ground state using the local stereographic projection of the spin nodes. We also provide a simple construction to extract the collective modes from symmetry considerations alone akin to the analysis of vibrational excitations of polyatomic molecules. Finally, we present a mapping between the spin-wave modes, and the wave functions of electrons in atoms, where the spherical symmetry is degraded by a crystal field. These results demonstrate the beautiful geometrical structure that underlies the dynamics of spinor condensates.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yc6xm-mpz93Renormalization group approach to oscillator synchronization
https://resolver.caltech.edu/CaltechAUTHORS:20091020-134924682
Authors: {'items': [{'id': 'Kogan-O', 'name': {'family': 'Kogan', 'given': 'Oleg'}}, {'id': 'Rogers-J-L', 'name': {'family': 'Rogers', 'given': 'Jeffrey L.'}}, {'id': 'Cross-M-C', 'name': {'family': 'Cross', 'given': 'M. C.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}]}
Year: 2009
DOI: 10.1103/PhysRevE.80.036206
We develop a renormalization group method to investigate synchronization clusters in a one-dimensional chain of nearest-neighbor coupled phase oscillators. The method is best suited for chains with strong disorder in the intrinsic frequencies and coupling strengths. The results are compared with numerical simulations of the chain dynamics and good agreement in several characteristics is found. We apply the renormalization group and simulations to Lorentzian distributions of intrinsic frequencies and couplings and investigate the statistics of the resultant cluster sizes and frequencies, as well as the dependence of the characteristic cluster length upon parameters of these Lorentzian distributions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/e1nq2-0fn39Universality in the one-dimensional chain of phase-coupled oscillators
https://resolver.caltech.edu/CaltechAUTHORS:20091124-144207656
Authors: {'items': [{'id': 'Lee-T-E', 'name': {'family': 'Lee', 'given': 'Tony E.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Cross-M-C', 'name': {'family': 'Cross', 'given': 'M. C.'}}, {'id': 'Kogan-O', 'name': {'family': 'Kogan', 'given': 'Oleg'}}, {'id': 'Rogers-J-L', 'name': {'family': 'Rogers', 'given': 'Jeffrey L.'}}]}
Year: 2009
DOI: 10.1103/PhysRevE.80.046210
We apply a recently developed renormalization-group (RG) method to study synchronization in a one-dimensional chain of phase-coupled oscillators in the regime of weak randomness. The RG predicts how oscillators with randomly distributed frequencies and couplings form frequency-synchronized clusters. Although the RG was originally intended for strong randomness, i.e., for distributions with long tails, we find good agreement with numerical simulations even in the regime of weak randomness. We use the RG flow to derive how the correlation length scales with the width of the coupling distribution in the limit of large coupling. This leads to the identification of a universality class of distributions with the same critical exponent v. We also find universal scaling for small coupling. Finally, we show that the RG flow is characterized by a universal approach to the unsynchronized fixed point, which provides physical insight into low-frequency clusters.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nvm0q-c4e20Investigating the superconductor-insulator transition in thin films using drag resistance: Theoretical analysis of a proposed experiment
https://resolver.caltech.edu/CaltechAUTHORS:20091223-133328679
Authors: {'items': [{'id': 'Zou-Y', 'name': {'family': 'Zou', 'given': 'Yue'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Yoon-J', 'name': {'family': 'Yoon', 'given': 'Jongsoo'}}]}
Year: 2009
DOI: 10.1103/PhysRevB.80.180503
The magnetically driven superconductor-insulator transition in amorphous thin films (e.g., InO and Ta) exhibits several mysterious phenomena, such as a putative metallic phase and a huge magnetoresistance peak. Unfortunately, several conflicting categories of theories, particularly quantum-vortex condensation, and normal region percolation, explain key observations equally well. We present a experimental setup, an amorphous thin-film bilayer, where a drag resistance measurement would clarify the role quantum vortices play in the transition, and hence decisively point to the correct picture. We provide a thorough analysis of the device, which shows that the vortex paradigm gives rise to a drag with an opposite sign and orders of magnitude larger than the drag measured if competing paradigms apply.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/12m9y-wdv11Interlayer Coherent Composite Fermi Liquid Phase in Quantum Hall Bilayers
https://resolver.caltech.edu/CaltechAUTHORS:20100114-143033701
Authors: {'items': [{'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Motrunich-O-I', 'name': {'family': 'Motrunich', 'given': 'Olexei I.'}, 'orcid': '0000-0001-8031-0022'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Fisher-Matthew-P-A', 'name': {'family': 'Fisher', 'given': 'Matthew P. A.'}}]}
Year: 2009
DOI: 10.1103/PhysRevLett.103.256403
We introduce an interlayer coherent composite Fermi liquid for ν=1/2+1/2 bilayers, in which interlayer Coulomb repulsion drives exciton condensation of composite fermions. As a result, composite fermions propagate coherently between layers—even though electrons do not—and form bonding and antibonding Fermi seas. This phase is compressible with respect to symmetric currents but quantum Hall-like in the counterflow channel. Quantum oscillations of the composite Fermi seas generate a new series of incompressible states at ν=p/[2(p±1)] per layer (p an integer), which is a bilayer analogue of Jain's sequence.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6sbfx-hf809Criticality and entanglement in random quantum systems
https://resolver.caltech.edu/CaltechAUTHORS:20100105-152508974
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Moore-J-E', 'name': {'family': 'Moore', 'given': 'J. E.'}}]}
Year: 2009
DOI: 10.1088/1751-8113/42/50/504010
We review studies of entanglement entropy in systems with quenched randomness, concentrating on universal behavior at strongly random quantum critical points. The disorder-averaged entanglement entropy provides insight into the quantum criticality of these systems and an understanding of their relationship to non-random ('pure') quantum criticality. The entanglement near many such critical points in one dimension shows a logarithmic divergence in subsystem size, similar to that in the pure case but with a different universal coefficient. Such universal coefficients are examples of universal critical amplitudes in a random system. Possible measurements are reviewed along with the one-particle entanglement scaling at certain Anderson localization transitions. We also comment briefly on higher dimensions and challenges for the future.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0xr9b-89881Quantum oscillations from Fermi arcs
https://resolver.caltech.edu/CaltechAUTHORS:20100120-105409610
Authors: {'items': [{'id': 'Pereg-Barnea-T', 'name': {'family': 'Pereg-Barnea', 'given': 'T.'}}, {'id': 'Weber-H', 'name': {'family': 'Weber', 'given': 'H.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Franz-M', 'name': {'family': 'Franz', 'given': 'M.'}}]}
Year: 2010
DOI: 10.1038/nphys1431
When a metal is subjected to a strong magnetic field B, nearly all measurable quantities show oscillations periodic in 1/B. Such quantum oscillations represent a canonical probe of the defining aspect of a metal, its Fermi surface. Recent breakthrough experiments demonstrating the existence of unambiguous quantum oscillations in a cuprate superconductor, YBa_(2)Cu_(3)O_(6.51), contradict the well-established result of many angle resolved photoemission studies, which consistently indicate 'Fermi arcs'—truncated segments of a Fermi surface—in the normal state of the cuprates. In this study, with the goal of reconciling the above disagreement, we introduce a mechanism for quantum oscillations that requires only finite segments of a Fermi surface. We show that oscillations periodic in 1/B can occur if the Fermi surface segments are terminated by a pairing gap and present arguments that these oscillations are in fact occurring in the cuprates.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/j7q3b-04196Vortex synchronization in Bose–Einstein condensates: a time-dependent Gross–Pitaevskii equation approach
https://resolver.caltech.edu/CaltechAUTHORS:20100518-103034288
Authors: {'items': [{'id': 'Barnett-R', 'name': {'family': 'Barnett', 'given': 'Ryan'}}, {'id': 'Chen-E', 'name': {'family': 'Chen', 'given': 'Edward'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2010
DOI: 10.1088/1367-2630/12/4/043004
In this work, we consider vortex lattices in rotating Bose–Einstein condensates composed of two species of bosons having different masses. Previously (Barnett et al 2008 New J. Phys. 10 043030), it was claimed that the vortices of the two species form bound pairs and the two vortex lattices lock. Remarkably, the two condensates and the external drive all rotate at different speeds owing to the disparity of the masses of the constituent bosons. In this paper, we study the system by solving the full two-component Gross–Pitaevskii equations numerically. Using this approach, we verify the stability of the putative locked state that is found to exist within a disc centered on the axis of rotation and that depends on the mass ratio of the two bosons. We also derive a refined estimate for the locking radius tailored to the experimentally relevant case of a harmonic trap and show that this agrees with the numerical results. Finally, we analyze in detail the rotation rates of the different components in the locked and unlocked regimes.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gxtzj-vg078Probing order parameter structure in iron-based superconductors using vortices
https://resolver.caltech.edu/CaltechAUTHORS:20100525-143325995
Authors: {'items': [{'id': 'Plamadeala-E', 'name': {'family': 'Plamadeala', 'given': 'Eugeniu'}}, {'id': 'Pereg-Barnea-T', 'name': {'family': 'Pereg-Barnea', 'given': 'T.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2010
DOI: 10.1103/PhysRevB.81.134513
Impurities, inevitably present in all samples, induce elastic transitions between quasiparticle states on the contours of constant energy. These transitions may be seen in Fourier-transformed scanning tunneling spectroscopy experiments, sorted by their momentum transfer. In a superconductor, anomalous scattering in the pairing channel may be introduced by magnetic field. When a magnetic field is applied, vortices act as additional sources of scattering. These additional transitions may enhance or suppress the impurity-induced scattering. We find that the vortex contribution to the transitions is sensitive to the momentum-space structure of the pairing function. In the iron-based superconductors, there are both electron and hole pockets at different regions of the Brillouin zone. Scattering processes therefore represent intrapocket or interpocket transitions, depending on the momentum transfer in the process. In this work we show that while in a simple s-wave superconductor all transitions are enhanced by vortex scattering, in an s_± superconductor only intrapocket transitions are affected. We suggest this effect as a probe for the existence of the sign change in the order parameter.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/38t4y-3gw70Superfluid-insulator transition of disordered bosons in one dimension
https://resolver.caltech.edu/CaltechAUTHORS:20100616-075847387
Authors: {'items': [{'id': 'Altman-E', 'name': {'family': 'Altman', 'given': 'Ehud'}}, {'id': 'Kafri-Y', 'name': {'family': 'Kafri', 'given': 'Yariv'}}, {'id': 'Polkovnikov-A', 'name': {'family': 'Polkovnikov', 'given': 'Anatoli'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2010
DOI: 10.1103/PhysRevB.81.174528
We study the superfluid-insulator transition in a one-dimensional system of interacting bosons, modeled as a disordered Josephson array, using a strong-randomness real-space renormalization-group technique. Unlike perturbative methods, this approach does not suffer from run-away flows and allows us to study the complete phase diagram. We show that the superfluid-insulator transition is always Kosterlitz-Thouless like in the way that length and time scales diverge at the critical point. Interestingly however, we find that the transition at strong disorder occurs at a nonuniversal value of the Luttinger parameter, which depends on the disorder strength. This result places the transition in a universality class different from the weak disorder transition first analyzed by Giamarchi and Schulz [Europhys. Lett. 3, 1287 (1987)]. While the details of the disorder potential are unimportant at the critical point, the type of disorder does influence the properties of the insulating phases. We find three classes of insulators which arise for different classes of disorder potential. For disorder only in the charging energies and Josephson coupling constants, at integer filling we find an incompressible but gapless Mott-glass phase. If both integer and half-integer filling factors are allowed then the corresponding phase is a random-singlet insulator, which has a divergent compressibility. Finally in a generic disorder potential the insulator is a Bose glass with a finite compressibility.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/e5qfr-0zp30Clausius-Clapeyron relations for first-order phase transitions in bilayer quantum Hall systems
https://resolver.caltech.edu/CaltechAUTHORS:20100615-143356094
Authors: {'items': [{'id': 'Zou-Yue', 'name': {'family': 'Zou', 'given': 'Yue'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Stern-A', 'name': {'family': 'Stern', 'given': 'Ady'}, 'orcid': '0000-0002-9493-268X'}, {'id': 'Eisenstein-J-P', 'name': {'family': 'Eisenstein', 'given': 'J. P.'}}]}
Year: 2010
DOI: 10.1103/PhysRevB.81.205313
A bilayer system of two-dimensional electron gases in a perpendicular magnetic field exhibits rich phenomena. At total filling factor ν_(tot)=1, as one increases the layer separation, the bilayer system goes from an interlayer-coherent exciton condensed state to an incoherent phase of, most likely, two decoupled composite-fermion Fermi liquids. Many questions still remain as to the nature of the transition between these two phases. Recent experiments have demonstrated that spin plays an important role in this transition. Assuming that there is a direct first-order transition between the spin-polarized interlayer-coherent quantum Hall state and spin partially polarized composite Fermi-liquid state, we calculate the phase boundary (d/l)_c as a function of parallel magnetic field, NMR/heat pulse, temperature, and density imbalance, and compare with experimental results. Remarkably good agreement is found between theory and various experiments.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/13j7k-kat24Majorana fermion chain at the quantum spin Hall edge
https://resolver.caltech.edu/CaltechAUTHORS:20100806-141508064
Authors: {'items': [{'id': 'Shivamoggi-V', 'name': {'family': 'Shivamoggi', 'given': 'V.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Moore-J-E', 'name': {'family': 'Moore', 'given': 'J. E.'}}]}
Year: 2010
DOI: 10.1103/PhysRevB.82.041405
We study a realization of a 1D chain of Majorana bound states at the interfaces between alternating ferromagnetic and superconducting regions at a quantum spin Hall insulator edge. In the limit of well-separated Majoranas, the system can be mapped to the transverse field Ising model. The disordered critical point can be reached by tuning the relative magnitude or phases of the ferromagnetic and superconducting order parameters. We compute the voltage dependence of the tunneling current from a metallic tip into the Majorana chain as a direct probe of the random critical state.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fk9mk-46v67Finding the Elusive Sliding Phase in the Superfluid-Normal Phase Transition Smeared by c-Axis Disorder
https://resolver.caltech.edu/CaltechAUTHORS:20100907-134630540
Authors: {'items': [{'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'Eugene'}}]}
Year: 2010
DOI: 10.1103/PhysRevLett.105.085302
We consider a stack of weakly Josephson coupled superfluid layers with c-axis disorder in the form of random superfluid stiffnesses and vortex fugacities in each layer as well as random interlayer coupling strengths. In the absence of disorder this system has a 3D XY type superfluid-normal phase transition as a function of temperature. We develop a functional renormalization group to treat the effects of disorder, and demonstrate that the disorder results in the smearing of the superfluid-normal phase transition via the formation of a Griffiths phase. Remarkably, in the Griffiths phase, the emergent power-law distribution of the interlayer couplings gives rise to a sliding Griffiths superfluid, with a finite stiffness in the a-b direction along the layers, and a vanishing stiffness perpendicular to it.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/z3hm5-jpz80Resistance in Superconductors
https://resolver.caltech.edu/CaltechAUTHORS:20101110-142749026
Authors: {'items': [{'id': 'Halperin-B-I', 'name': {'family': 'Halperin', 'given': 'Bertrand I.'}, 'orcid': '0000-0002-6999-1039'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'Eugene'}}]}
Year: 2010
DOI: 10.1142/S021797921005644X
In this pedagogical review, we discuss how electrical resistance can arise in superconductors. Starting with the idea of the superconducting order parameter as a condensate wave function, we introduce vortices as topological excitations with quantized phase winding, and we show how phase slips occur when vortices cross the sample. Superconductors exhibit non-zero electrical resistance under circumstances where phase slips occur at a finite rate. For one-dimensional superconductors or Josephson junctions, phase slips can occur at isolated points in space-time. Phase slip rates may be controlled by thermal activation over a free-energy barrier, or in some circumstances, at low temperatures, by quantum tunneling through a barrier. We present an overview of several phenomena involving vortices that have direct implications for the electrical resistance of superconductors, including the Berezinskii-Kosterlitz-Thouless transition for vortex-proliferation in thin films, and the effects of vortex pinning in bulk type II superconductors on the nonlinear resistivity of these materials in an applied magnetic field. We discuss how quantum fluctuations can cause phase slips and review the non-trivial role of dissipation on such fluctuations. We present a basic picture of the superconductor-to-insulator quantum phase transitions in films, wires, and Josephson junctions. We point out related problems in superfluid helium films and systems of ultra-cold trapped atoms. While our emphasis is on theoretical concepts, we also briefly describe experimental results, and we underline some of the open questions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kse1z-c6j35Vortices and the entrainment transition in the two-dimensional Kuramoto model
https://resolver.caltech.edu/CaltechAUTHORS:20100920-105131252
Authors: {'items': [{'id': 'Lee-T-E', 'name': {'family': 'Lee', 'given': 'Tony E.'}}, {'id': 'Tam-H', 'name': {'family': 'Tam', 'given': 'Heywood'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Rogers-J-L', 'name': {'family': 'Rogers', 'given': 'Jeffrey L.'}}, {'id': 'Cross-M-C', 'name': {'family': 'Cross', 'given': 'M. C.'}}]}
Year: 2010
DOI: 10.1103/PhysRevE.82.036202
We study synchronization in the two-dimensional lattice of coupled phase oscillators with random intrinsic frequencies. When the coupling K is larger than a threshold K_E, there is a macroscopic cluster of frequency-synchronized oscillators. We explain why the macroscopic cluster disappears at K_E. We view the system in terms of vortices, since cluster boundaries are delineated by the motion of these topological defects. In the entrained phase (K>K_E), vortices move in fixed paths around clusters, while in the unentrained phase (Khttps://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/mrbrb-p9g51Theoretical analysis of drag resistance in amorphous thin films exhibiting superconductor-insulator transitions
https://resolver.caltech.edu/CaltechAUTHORS:20101025-114133254
Authors: {'items': [{'id': 'Zou-Y', 'name': {'family': 'Zou', 'given': 'Yue'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Yoon-J', 'name': {'family': 'Yoon', 'given': 'Jongsoo'}}]}
Year: 2010
DOI: 10.1103/PhysRevB.82.104515
The magnetical field tuned superconductor-insulator transition in amorphous thin films, e.g., Ta and InO,
exhibits a range of yet unexplained curious phenomena, such as a putative low-resistance metallic phase
intervening the superconducting and the insulating phase, and a huge peak in the magnetoresistance at large
magnetic field. Qualitatively, the phenomena can be explained equally well within several significantly different
pictures, particularly the condensation of quantum vortex liquid, and the percolation of superconducting
islands embedded in normal region. Recently, we proposed and analyzed a distinct measurement in Y. Zou,
G. Refael, and J. Yoon, Phys. Rev. B 80, 180503 (2009) that should be able to decisively point to the correct
picture: a drag resistance measurement in an amorphous thin-film bilayer setup. Neglecting interlayer tunneling,
we found that the drag resistance within the vortex paradigm has opposite sign and is orders of magnitude
larger than that in competing paradigms. For example, two identical films as in G. Sambandamurthy, L. W.
Engel, A. Johansson, and D. Shahar, Phys. Rev. Lett. 92, 107005 _2004_ with 25 nm layer separation at
0.07 K would produce a drag resistance ~10^(−4) Ω according the vortex theory but only ~10^(−12) Ω for the
percolation theory. We provide details of our theoretical analysis of the drag resistance within both paradigms
and report some results as well.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/agg6a-mz722Helical Liquids and Majorana Bound States in Quantum Wires
https://resolver.caltech.edu/CaltechAUTHORS:20101109-122846688
Authors: {'items': [{'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2010
DOI: 10.1103/PhysRevLett.105.177002
We show that the combination of spin-orbit coupling with a Zeeman field or strong interactions may lead to the formation of a helical electron liquid in single-channel quantum wires, with spin and velocity perfectly correlated. We argue that zero-energy Majorana bound states are formed in various situations when such wires are situated in proximity to a conventional s-wave superconductor. This occurs when the external magnetic field, the superconducting gap, or, most simply, the chemical potential vary along the wire. These Majorana states do not require the presence of a vortex in the system. Experimental consequences of the helical liquid and the Majorana states are also discussed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8gcth-pa111Bulk metals with helical surface states
https://resolver.caltech.edu/CaltechAUTHORS:20101215-110525362
Authors: {'items': [{'id': 'Bergman-D-L', 'name': {'family': 'Bergman', 'given': 'Doron L.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2010
DOI: 10.1103/PhysRevB.82.195417
In the flurry of experiments looking for topological insulator materials, it has been recently discovered that some bulk metals very close to topological insulator electronic states support the same topological surface states that are the defining characteristic of the topological insulator. First observed in spin-polarized angle resolved photoemission spectroscopy (ARPES) in Sb [D. Hsieh et al., Science 323, 919 (2009)], the helical surface states in the metallic systems appear to be robust to at least mild disorder. We present here a theoretical investigation of the nature of these "helical metals"—bulk metals with helical surface states. We explore how the surface and bulk states can mix, in both clean and disordered systems. Using the Fano model, we discover that in a clean system, the helical surface states are not simply absorbed by hybridization with a nontopological parasitic metallic band. Instead, they are pushed away from overlapping in momentum and energy with the bulk states, leaving behind a finite-lifetime surface resonance in the bulk energy band. Furthermore, the hybridization may lead in some cases to multiplied surface-state bands, in all cases retaining the helical characteristic. Weak disorder leads to very similar effects—surface states are pushed away from the energy bandwidth of the bulk, leaving behind a finite-lifetime surface resonance in place of the original surface states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7t4d7-74y98Topological Anderson Insulator in Three Dimensions
https://resolver.caltech.edu/CaltechAUTHORS:20101214-105429377
Authors: {'items': [{'id': 'Guo-H-M', 'name': {'family': 'Guo', 'given': 'H.-M.'}}, {'id': 'Rosenberg-G', 'name': {'family': 'Rosenberg', 'given': 'G.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Franz-M', 'name': {'family': 'Franz', 'given': 'M.'}}]}
Year: 2010
DOI: 10.1103/PhysRevLett.105.216601
We show that disorder, when sufficiently strong, can transform an ordinary metal with strong spin-orbit
coupling into a strong topological "Anderson" insulator, a new topological phase of quantum matter in
three dimensions characterized by disordered insulating bulk and topologically protected conducting
surface states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/sh9jq-2w304Particle-hole symmetric localization in optical lattices using time modulated random on-site potentials
https://resolver.caltech.edu/CaltechAUTHORS:20110328-082217476
Authors: {'items': [{'id': 'Zou-Y', 'name': {'family': 'Zou', 'given': 'Yue'}}, {'id': 'Barnett-R', 'name': {'family': 'Barnett', 'given': 'Ryan'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2010
DOI: 10.1103/PhysRevB.82.224205
The random hopping models exhibit many fascinating features, such as diverging localization length and
density of states as energy approaches the band center due to its particle-hole symmetry. Nevertheless, such
models are yet to be realized experimentally because the particle-hole symmetry is easily destroyed by diagonal
disorder. Here we propose that a pure random hopping model can be effectively realized in ultracold
atoms by modulating a disordered onsite potential in particular frequency ranges. This idea is motivated by the
recent development of the phenomena called "dynamical localization" or "coherent destruction of tunneling."
Investigating the application of this idea in one dimension, we find that if the oscillation frequency of the
disorder potential is gradually increased from zero to infinity, one can tune a noninteracting system from an
Anderson insulator to a random hopping model with diverging localization length at the band center, and
eventually to a uniform-hopping tight-binding model.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/r0d6p-ayb37Dynamic Stimulation of Quantum Coherence in Systems of Lattice Bosons
https://resolver.caltech.edu/CaltechAUTHORS:20110523-102744616
Authors: {'items': [{'id': 'Robertson-A', 'name': {'family': 'Robertson', 'given': 'Andrew'}}, {'id': 'Galitski-V-M', 'name': {'family': 'Galitski', 'given': 'Victor M.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2011
DOI: 10.1103/PhysRevLett.106.165701
Thermal fluctuations tend to destroy long-range phase correlations. Consequently, bosons in a lattice will undergo a transition from a phase-coherent superfluid as the temperature rises. Contrary to common intuition, however, we show that nonequilibrium driving can be used to reverse this thermal decoherence. This is possible because the energy distribution at equilibrium is rarely optimal for the manifestation of a given quantum property. We demonstrate this in the Bose-Hubbard model by calculating the nonequilibrium spatial correlation function with periodic driving. We show that the nonequilibrium phase boundary between coherent and incoherent states at finite bath temperatures can be made qualitatively identical to the familiar zero-temperature phase diagram, and we discuss the experimental manifestation of this phenomenon in cold atoms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/v5hpe-2sy82Non-Abelian statistics and topological quantum information processing in 1D wire networks
https://resolver.caltech.edu/CaltechAUTHORS:20110524-084153167
Authors: {'items': [{'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}, {'id': 'Fisher-Matthew-P-A', 'name': {'family': 'Fisher', 'given': 'Matthew P. A.'}}]}
Year: 2011
The synthesis of a quantum computer remains an ongoing challenge in modern physics. Whereas decoherence stymies most approaches, topological quantum computation schemes evade decoherence at the hardware level by storing quantum information non-locally. Here we establish that a key operation—braiding of non-Abelian anyons—can be implemented using one-dimensional semiconducting wires. Such wires can be driven into a topological phase supporting long-sought particles known as Majorana fermions that can encode topological qubits. We show that in wire networks, Majorana fermions can be meaningfully braided by simply adjusting gate voltages, and that they exhibit non-Abelian statistics like vortices in a p+ip superconductor. We propose experimental set-ups that enable probing of the Majorana fusion rules and the efficient exchange of arbitrary numbers of Majorana fermions. This work should open a new direction in topological quantum computation that benefits from physical transparency and experimental feasibility.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cbske-gh304Floquet topological insulator in semiconductor quantum wells
https://resolver.caltech.edu/CaltechAUTHORS:20110621-100028234
Authors: {'items': [{'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Galitski-V', 'name': {'family': 'Galitski', 'given': 'Victor'}}]}
Year: 2011
DOI: 10.1038/nphys1926
Topological phases of matter have captured our imagination over the past few years, with tantalizing properties such as robust edge modes and exotic non-Abelian excitations, and potential applications ranging from semiconductor spintronics to topological quantum computation. Despite recent advancements in the field, our ability to control topological transitions remains limited, and usually requires changing material or structural properties. We show, using Floquet theory, that a topological state can be induced in a semiconductor quantum well, initially in the trivial phase. This can be achieved by irradiation with microwave frequencies, without changing the well structure, closing the gap and crossing the phase transition. We show that the quasi-energy spectrum exhibits a single pair of helical edge states. We discuss the necessary experimental parameters for our proposal. This proposal provides an example and a proof of principle of a new non-equilibrium topological state, the Floquet topological insulator, introduced in this paper.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/2h34p-pca10Majorana Fermions in Equilibrium and in Driven Cold-Atom Quantum Wires
https://resolver.caltech.edu/CaltechAUTHORS:20110621-093218853
Authors: {'items': [{'id': 'Jiang-Liang', 'name': {'family': 'Jiang', 'given': 'Liang'}, 'orcid': '0000-0002-0000-9342'}, {'id': 'Kitagawa-Takuya', 'name': {'family': 'Kitagawa', 'given': 'Takuya'}}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Akhmerov-', 'name': {'family': 'Akhmerov', 'given': 'A. R.'}}, {'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Cirac-J-I', 'name': {'family': 'Cirac', 'given': 'J. Ignacio'}}, {'id': 'Demler-E-A', 'name': {'family': 'Demler', 'given': 'Eugene'}}, {'id': 'Lukin-M-D', 'name': {'family': 'Lukin', 'given': 'Mikhail D.'}, 'orcid': '0000-0002-8658-1007'}, {'id': 'Zoller-P', 'name': {'family': 'Zoller', 'given': 'Peter'}}]}
Year: 2011
DOI: 10.1103/PhysRevLett.106.220402
We introduce a new approach to create and detect Majorana fermions using optically trapped 1D fermionic atoms. In our proposed setup, two internal states of the atoms couple via an optical Raman transition—simultaneously inducing an effective spin-orbit interaction and magnetic field—while a background molecular BEC cloud generates s-wave pairing for the atoms. The resulting cold-atom quantum wire supports Majorana fermions at phase boundaries between topologically trivial and nontrivial regions, as well as "Floquet Majorana fermions" when the system is periodically driven. We analyze experimental parameters, detection schemes, and various imperfections.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/bqkpg-svp12Weber Blockade Theory of Magnetoresistance Oscillations in Superconducting Strips
https://resolver.caltech.edu/CaltechAUTHORS:20110712-110828545
Authors: {'items': [{'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Goldbart-P-M', 'name': {'family': 'Goldbart', 'given': 'Paul M.'}}]}
Year: 2011
DOI: 10.1103/PhysRevLett.107.017002
Recent experiments on the conductance of thin, narrow superconducting strips have found periodic fluctuations, as a function of the perpendicular magnetic field, with a period corresponding to approximately two flux quanta per strip area [A. Johansson et al., Phys. Rev. Lett. 95, 116805 (2005)]. We argue that the low-energy degrees of freedom responsible for dissipation correspond to vortex motion. Using vortex-charge duality, we show that the superconducting strip behaves as the dual of a quantum dot, with the vortices, magnetic field, and bias current respectively playing the roles of the electrons, gate voltage, and source-drain voltage. In the bias-current versus magnetic-field plane, the strip conductance displays regions of small vortex conductance (i.e., small electrical resistance) that we term "Weber blockade" diamonds, which are dual to Coulomb blockade diamonds in quantum dots.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kk0ys-35x56A Mott Glass to Superfluid Transition for Random Bosons in Two Dimensions
https://resolver.caltech.edu/CaltechAUTHORS:20111031-090402654
Authors: {'items': [{'id': 'Iyer-S', 'name': {'family': 'Iyer', 'given': 'S.'}}, {'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'D.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}]}
Year: 2011
DOI: 10.48550/arXiv.1110.3338
We study the zero temperature superfluid-insulator transition for a two-dimensional model of
interacting, lattice bosons in the presence of quenched disorder and particle-hole symmetry. We
follow the approach of a recent series of papers by Altman, Kafri, Polkovnikov, and Refael, in which
the strong disorder renormalization group is used to study disordered bosons in one dimension.
Adapting this method to two dimensions, we study several different species of disorder and uncover
universal features of the superfluid-insulator transition. In particular, we locate an unstable finite
disorder fixed point that governs the transition between the superfluid and a gapless, glassy insulator.
We present numerical evidence that this glassy phase is the incompressible Mott glass and that the
transition from this phase to the superfluid is driven by percolation-type process. Finally, we provide
estimates of the critical exponents governing this transition.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/r34va-8s370Energy Partitioning of Tunneling Currents into Luttinger Liquids
https://resolver.caltech.edu/CaltechAUTHORS:20111122-110805328
Authors: {'items': [{'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Glazman-L-I', 'name': {'family': 'Glazman', 'given': 'Leonid I.'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2011
DOI: 10.1103/PhysRevLett.107.176403
Tunneling of electrons of definite chirality into a quantum wire creates counterpropagating excitations, carrying both charge and energy. We find that the partitioning of energy is qualitatively different from that of charge. The partition ratio of energy depends on the excess energy of the tunneling electrons (controlled by the applied bias) and on the interaction strength within the wire (characterized by the Luttinger-liquid parameter κ), while the partitioning of charge is fully determined by κ. Moreover, unlike for charge currents, the partitioning of energy current should manifest itself in dc experiments on wires contacted by conventional (Fermi-liquid) leads.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/sp7k2-ne403Gapless Excitations in Strongly Fluctuating Superconducting Wires
https://resolver.caltech.edu/CaltechAUTHORS:20111216-150959334
Authors: {'items': [{'id': 'Meidan-D', 'name': {'family': 'Meidan', 'given': 'Dganit'}}, {'id': 'Rosenow-B', 'name': {'family': 'Rosenow', 'given': 'Bernd'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2011
DOI: 10.1103/PhysRevLett.107.227004
We study the low-temperature tunneling density of states of thin wires where superconductivity is destroyed through quantum phase-slip proliferation. Although this regime is believed to behave as an insulator, we show that for a large temperature range this phase is characterized by a conductivity falling off at most linearly with temperature, and has a gapless excitation spectrum. This novel conducting phase results from electron-electron interaction induced pair breaking. Also, it may help clarify the low-temperature metallic features found in films and wires whose bulk realization is superconducting.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4yetq-q2796Unconventional Josephson Signatures of Majorana Bound States
https://resolver.caltech.edu/CaltechAUTHORS:20120104-113454842
Authors: {'items': [{'id': 'Jiang-Liang', 'name': {'family': 'Jiang', 'given': 'Liang'}, 'orcid': '0000-0002-0000-9342'}, {'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2011
DOI: 10.1103/PhysRevLett.107.236401
A junction between two topological superconductors containing a pair of Majorana fermions exhibits a "fractional" Josephson effect, 4π periodic in the superconductors' phase difference. An additional fractional Josephson effect, however, arises when the Majorana fermions are spatially separated by a superconducting barrier. This new term gives rise to a set of Shapiro steps which are essentially absent without Majorana modes and therefore provides a unique signature for these exotic states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/cxmwp-zsg75Manipulating Majorana fermions using supercurrents
https://resolver.caltech.edu/CaltechAUTHORS:20120206-102258105
Authors: {'items': [{'id': 'Romito-A', 'name': {'family': 'Romito', 'given': 'Alessandro'}}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2012
DOI: 10.1103/PhysRevB.85.020502
Topological insulator edges and spin-orbit-coupled quantum wires in proximity to s-wave superconductors can be tuned through a topological quantum phase transition by a Zeeman field. Here we show that a supercurrent flowing in the s-wave superconductor also drives such a transition. We propose to use this mechanism to generate and manipulate Majorana fermions that localize at domain walls between topological and nontopological regions of an edge or wire. In quantum wires, this method carries the added benefit that a supercurrent reduces the critical Zeeman field at which the topological phase appears.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yvkvs-3n480Inducing topological order in a honeycomb lattice
https://resolver.caltech.edu/CaltechAUTHORS:20120321-105734817
Authors: {'items': [{'id': 'Pereg-Barnea-T', 'name': {'family': 'Pereg-Barnea', 'given': 'T.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}]}
Year: 2012
DOI: 10.1103/PhysRevB.85.075127
We explore the possibility of inducing a topological insulator phase in a honeycomb lattice lacking spin-orbit interaction using a metallic (or Fermi gas) environment. The lattice and the metallic environment interact through a density-density interaction without particle tunneling, and integrating out the metallic environment produces a honeycomb sheet with in-plane oscillating long-ranged interactions. We find the ground state of the interacting system in a variational mean-field method and show that the Fermi wave vector k_F of the metal determines which phase occurs in the honeycomb lattice sheet. This is analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism in which the metal's k_F determines the interaction profile as a function of the distance. Tuning k_F and the interaction strength may lead to a variety of ordered phases, including a topological insulator and anomalous quantum-Hall states with complex next-nearest-neighbor hopping, as in the Haldane and the Kane-Mele model. We estimate the required range of parameters needed for the topological state and find that the Fermi vector of the metallic gate should be of the order of 3π/8a (with a being the graphene lattice constant). The net coupling between the layers, which includes screening in the metal, should be of the order of the honeycomb lattice bandwidth. This configuration should be most easily realized in a cold-atoms setting with two interacting Fermionic species.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/86mty-znh62Mott glass to superfluid transition for random bosons in two dimensions
https://resolver.caltech.edu/CaltechAUTHORS:20120406-125838850
Authors: {'items': [{'id': 'Iyer-S', 'name': {'family': 'Iyer', 'given': 'S.'}}, {'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'D.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}]}
Year: 2012
DOI: 10.1103/PhysRevB.85.094202
We study the zero-temperature superfluid-insulator transition for a two-dimensional model of interacting, lattice bosons in the presence of quenched disorder and particle-hole symmetry. We follow the approach of a recent series of papers by Altman, Kafri, Polkovnikov, and Refael, in which the strong disorder renormalization group is used to study disordered bosons in one dimension. Adapting this method to two dimensions, we study several different species of disorder and uncover universal features of the superfluid-insulator transition. In particular, we locate an unstable finite disorder fixed point that governs the transition between the superfluid and a gapless, glassy insulator. We present numerical evidence that this glassy phase is the incompressible Mott glass and that the transition from this phase to the superfluid is driven by a percolation-type process. Finally, we provide estimates of the critical exponents governing this transition.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/29b51-apt52Adiabatic manipulations of Majorana fermions in a three-dimensional network of quantum wires
https://resolver.caltech.edu/CaltechAUTHORS:20120502-145534850
Authors: {'items': [{'id': 'Halperin-B-I', 'name': {'family': 'Halperin', 'given': 'Bertrand I.'}, 'orcid': '0000-0002-6999-1039'}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Stern-A', 'name': {'family': 'Stern', 'given': 'Ady'}, 'orcid': '0000-0002-9493-268X'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2012
DOI: 10.1103/PhysRevB.85.144501
It has been proposed that localized zero-energy Majorana states can be realized in a two-dimensional network of quasi-one-dimensional semiconductor wires that are proximity coupled to a bulk superconductor. The wires should have strong spin-orbit coupling with appropriate symmetry, and their electrons should be partially polarized by a strong Zeeman field. Then, if the Fermi level is in an appropriate range, the wire can be in a topological superconducting phase, with Majorana states that occur at wire ends and at Y junctions, where three topological superconductor segments may be joined. Here we generalize these ideas to consider a three-dimensional network. The positions of Majorana states can be manipulated, and their non-Abelian properties made visible, by using external gates to selectively deplete portions of the network or by physically connecting and redividing wire segments. Majorana states can also be manipulated by reorientations of the Zeeman field on a wire segment, by physically rotating the wire about almost any axis, or by evolution of the phase of the order parameter in the proximity-coupled superconductor. We show how to keep track of sign changes in the zero-energy Hilbert space during adiabatic manipulations by monitoring the evolution of each Majorana state separately, rather than keeping track of the braiding of all possible pairs. This has conceptual advantages in the case of a three-dimensional network, and may be computationally useful even in two dimensions, if large numbers of Majorana sites are involved.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jzgnz-mg350Strong-disorder renormalization for interacting non-Abelian anyon systems in two dimensions
https://resolver.caltech.edu/CaltechAUTHORS:20120515-151935679
Authors: {'items': [{'id': 'Laumann-C-R', 'name': {'family': 'Laumann', 'given': 'C. R.'}}, {'id': 'Huse-D-A', 'name': {'family': 'Huse', 'given': 'D. A.'}}, {'id': 'Ludwig-A-W-W', 'name': {'family': 'Ludwig', 'given': 'A. W. W.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Trebst-S', 'name': {'family': 'Trebst', 'given': 'S.'}}, {'id': 'Troyer-M', 'name': {'family': 'Troyer', 'given': 'M.'}}]}
Year: 2012
DOI: 10.1103/PhysRevB.85.224201
We consider the effect of quenched spatial disorder on systems of interacting, pinned non-Abelian anyons as might arise in disordered Hall samples at filling fractions ν=5/2 or ν=12/5. In one spatial dimension, such disordered anyon models have previously been shown to exhibit a hierarchy of infinite randomness phases. Here, we address systems in two spatial dimensions and report on the behavior of Ising and Fibonacci anyons under the numerical strong-disorder renormalization group (SDRG). In order to manage the topology-dependent interactions generated during the flow, we introduce a planar approximation to the SDRG treatment. We characterize this planar approximation by studying the flow of disordered hard-core bosons and the transverse field Ising model, where it successfully reproduces the known infinite randomness critical point with exponent ψ ≈ 0.49. Our main conclusion for disordered anyon models in two spatial dimensions is that systems of Ising anyons as well as systems of Fibonacci anyons do not realize infinite randomness phases, but flow back to weaker disorder under the numerical SDRG treatment.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5c512-dw803Electrical Manipulation of Majorana Fermions in an Interdigitated Superconductor-Ferromagnet Device
https://resolver.caltech.edu/CaltechAUTHORS:20121101-101619309
Authors: {'items': [{'id': 'Lee-Shu-Ping', 'name': {'family': 'Lee', 'given': 'Shu-Ping'}}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2012
DOI: 10.1103/PhysRevLett.109.126403
We show that a topological phase supporting Majorana fermions can form in a two-dimensional electron gas (2DEG) adjacent to an interdigitated superconductor-ferromagnet structure. An advantage of this setup is that the 2DEG can induce the required Zeeman splitting and superconductivity from a single interface, allowing one to utilize a wide class of 2DEGs including the surface states of bulk InAs. We demonstrate that the interdigitated device supports a robust topological phase when the finger spacing λ is smaller than half of the Fermi wavelength λ_F. In this regime, the electrons effectively see a "smeared" Zeeman splitting and pairing field despite the interdigitation. The topological phase survives even in the opposite limit λ>λ_F/2, although with a reduced bulk gap. We describe how to electrically generate a vortex in this setup to trap a Majorana mode, and predict an anomalous Fraunhofer pattern that provides a sharp signature of chiral Majorana edge states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/yw3zj-jc791Ettingshausen effect due to Majorana modes
https://resolver.caltech.edu/CaltechAUTHORS:20121108-091556878
Authors: {'items': [{'id': 'Hou-C-Y', 'name': {'family': 'Hou', 'given': 'C.-Y'}}, {'id': 'Shtengel-K', 'name': {'family': 'Shtengel', 'given': 'K.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Goldbart-P-M', 'name': {'family': 'Goldbart', 'given': 'P. M.'}}]}
Year: 2012
DOI: 10.1088/1367-2630/14/10/105005
The presence of Majorana zero-energy modes at vortex cores in a topological superconductor implies that each vortex carries an extra entropy s_0, given by (k_B/2)ln 2, that is independent of temperature. By utilizing this special property of Majorana modes, the edges of a topological superconductor can be cooled (or heated) by the motion of the vortices across the edges. As vortices flow in the transverse direction with respect to an external imposed supercurrent, due to the Lorentz force, a thermoelectric effect analogous to the Ettingshausen effect is expected to occur between opposing edges. We propose an experiment to observe this thermoelectric effect, which could directly probe the intrinsic entropy of Majorana zero-energy modes.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fmas8-8qk41Fractionalizing Majorana fermions: non-Abelian Statistics on the Edges of Abelian Quantum Hall States
https://resolver.caltech.edu/CaltechAUTHORS:20120430-073146103
Authors: {'items': [{'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Berg-E', 'name': {'family': 'Berg', 'given': 'Erez'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Stern-A', 'name': {'family': 'Stern', 'given': 'Ady'}, 'orcid': '0000-0002-9493-268X'}]}
Year: 2012
DOI: 10.1103/PhysRevX.2.041002
We study the non-abelian statistics characterizing systems where counterpropagating gapless modes on the edges of fractional quantum Hall states are gapped by proximity coupling to superconductors and ferromagnets. The most transparent example is that of a fractional quantum spin Hall state, in which electrons of one spin direction occupy a fractional quantum Hall state of
v = 1/m, while electrons of the opposite spin occupy a similar state with v = -1/m. However, we also propose other examples of such systems, which are easier to realize experimentally. We find that each interface between a region on the edge coupled to a superconductor and a region coupled to a ferromagnet corresponds to a non-Abelian anyon of quantum dimension √(2m). We calculate the
unitary transformations that are associated with braiding of these anyons, and show that they are able to realize a richer set of non-Abelian representations of the braid group than the set realized by non-abelian anyons based on Majorana fermions. We carry out this calculation both explicitly and by applying general considerations. Finally, we show that topological manipulations with these
anyons cannot realize universal quantum computation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6qzsm-pyn88Thermodynamic measure of the magnetoelectric coupling in a three-dimensional topological insulator
https://resolver.caltech.edu/CaltechAUTHORS:20120130-132632571
Authors: {'items': [{'id': 'Bergman-D-L', 'name': {'family': 'Bergman', 'given': 'Doron L.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.87.024202
We show that the magnetoelectric coupling in three-dimensional (strong) topological insulators is related to a second derivative of the bulk magnetization. The formula we derive is the nonlinear-response analog of the Streda formula for Hall conductivity [Streda, J. Phys. C 15, L717 (1982)], which relates the Hall conductivity to the derivative of the magnetization with respect to the chemical potential. Our finding allows one to extract the magnetoelectric coefficient by measuring the magnetization, while varying the chemical potential and one more perturbing field. The relation we find also makes transparent the effect of disorder on the magnetoelectric response, which occurs only through the density of states, and has no effect when the system is gapped.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/3p1vv-myv71Magneto-Josephson effects in junctions with Majorana bound states
https://resolver.caltech.edu/CaltechAUTHORS:20130326-135438324
Authors: {'items': [{'id': 'Jiang-Liang', 'name': {'family': 'Jiang', 'given': 'Liang'}, 'orcid': '0000-0002-0000-9342'}, {'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Brataas-A', 'name': {'family': 'Brataas', 'given': 'Arne'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.87.075438
We investigate 1D quantum systems that support Majorana bound states at interfaces between topologically distinct regions. In particular, we show that there exists a duality between particle-hole and spin degrees of freedom in certain spin-orbit-coupled 1D platforms such as topological insulator edges. This duality results in a spin analog of previously explored "fractional Josephson effects"—that is, the spin current flowing across a magnetic junction exhibits 4π periodicity in the relative magnetic field angle across the junction. Furthermore, the interplay between the particle-hole and spin degrees of freedom results in unconventional magneto-Josephson effects, such that the Josephson charge current is a function of the magnetic field orientation with periodicity 4π.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9g9zp-ar906Disordered topological metals
https://resolver.caltech.edu/CaltechAUTHORS:20130425-082200743
Authors: {'items': [{'id': 'Meyer-J-S', 'name': {'family': 'Meyer', 'given': 'Julia S.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.87.104202
Topological behavior can be masked when disorder is present. A topological insulator, either intrinsic or interaction induced, may turn gapless when sufficiently disordered. Nevertheless, the metallic phase that emerges once a topological gap closes retains several topological characteristics. By considering the self-consistent disorder-averaged Green function of a topological insulator, we derive the condition for gaplessness. We show that the edge states survive in the gapless phase as edge resonances and that, similar to a doped topological insulator, the disordered topological metal also has a finite, but nonquantized topological index. We then consider the disordered Mott topological insulator. We show that within mean-field theory, the disordered Mott topological insulator admits a phase where the symmetry-breaking order parameter remains nonzero but the gap is closed, in complete analogy to "gapless superconductivity" due to magnetic disorder.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/z01wd-fjc41Many-body localization in a quasiperiodic system
https://resolver.caltech.edu/CaltechAUTHORS:20130510-141525888
Authors: {'items': [{'id': 'Iyer-S', 'name': {'family': 'Iyer', 'given': 'Shankar'}}, {'id': 'Oganesyan-V', 'name': {'family': 'Oganesyan', 'given': 'Vadim'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Huse-D-A', 'name': {'family': 'Huse', 'given': 'David A.'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.87.134202
Recent theoretical and numerical evidence suggests that localization can survive in disordered many-body systems with very high energy density, provided that interactions are sufficiently weak. Stronger interactions can destroy localization, leading to a so-called many-body localization transition. This dynamical phase transition is relevant to questions of thermalization in extended quantum systems far from the zero-temperature limit. It separates a many-body localized phase, in which localization prevents transport and thermalization, from a conducting ("ergodic") phase in which the usual assumptions of quantum statistical mechanics hold. Here, we present numerical evidence that many-body localization also occurs in models without disorder but rather a quasiperiodic potential. In one dimension, these systems already have a single-particle localization transition, and we show that this transition becomes a many-body localization transition upon the introduction of interactions. We also comment on possible relevance of our results to experimental studies of many-body dynamics of cold atoms and nonlinear light in quasiperiodic potentials.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/b02bj-w0f61Transport through a disordered topological-metal strip
https://resolver.caltech.edu/CaltechAUTHORS:20130725-082656877
Authors: {'items': [{'id': 'Junck-A', 'name': {'family': 'Junck', 'given': 'Alexandra'}}, {'id': 'Kim-K-W', 'name': {'family': 'Kim', 'given': 'Kun W.'}}, {'id': 'Bergman-D-L', 'name': {'family': 'Bergman', 'given': 'Doron L.'}}, {'id': 'Pereg-Barnea-T', 'name': {'family': 'Pereg-Barnea', 'given': 'T.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.87.235114
Features of a topological phase, and edge states in particular, may be obscured by overlapping in energy with a trivial conduction band. The topological nature of such a conductor, however, is revealed in its transport properties, especially in the presence of disorder. In this work, we explore the conductance behavior of such a system with disorder present, and contrast it with the quantized conductance in an ideal two-dimensional topological insulator. Our analysis relies on numerics on a lattice system and analytics on a simple toy model. Interestingly, we find that as disorder is increased from zero, the edge conductivity initially falls from its quantized value; yet, as disorder continues to increase, the conductivity recovers, and saturates at a value slightly below the quantized value of the clean system. We discuss how this effect can be understood from the tendency of the bulk states to localize, while the edge states remain delocalized.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/z2d6m-4xt15Topological Floquet Spectrum in Three Dimensions via a Two-Photon Resonance
https://resolver.caltech.edu/CaltechAUTHORS:20120515-144047298
Authors: {'items': [{'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Bergman-D-L', 'name': {'family': 'Bergman', 'given': 'Doron L.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Galitski-V', 'name': {'family': 'Galitski', 'given': 'Victor'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.87.235131
Three dimensional (3D) topological insulators display an array of unique properties such as single Dirac-cone surface states and a strong magnetoelectric effect. Here we show how a 3D topological spectrum can be induced in a trivial insulator by a periodic drive and, in particular, using electromagnetic radiation. In contrast to the two-dimensional analog, we show that a two-photon resonance is required to transform an initially unremarkable band structure into a topological Floquet spectrum. We provide an intuitive, geometrical picture, alongside a numerical solution of a driven lattice model featuring a single surface Dirac mode. Also, we show that the polarization and frequency of the driving electromagnetic field control the details of the surface modes and particularly the Dirac mass. Specific experimental realizations of the 3D Floquet topological insulator are proposed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ags4w-qfg70Adiabatic Quantum Motors
https://resolver.caltech.edu/CaltechAUTHORS:20130909-112144198
Authors: {'items': [{'id': 'Bustos-Marún-R', 'name': {'family': 'Bustos-Marún', 'given': 'Raúl'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2013
DOI: 10.1103/PhysRevLett.111.060802
When parameters are varied periodically, charge can be pumped through a mesoscopic conductor without applied bias. Here, we consider the inverse effect in which a transport current drives a periodic variation of an adiabatic degree of freedom. This provides a general operating principle for adiabatic quantum motors which we discuss here in general terms. We relate the work performed per cycle on the motor degree of freedom to characteristics of the underlying quantum pump and discuss the motors' efficiency. Quantum motors based on chaotic quantum dots operate solely due to quantum interference, and motors based on Thouless pumps have ideal efficiency.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jj3w2-7rt60Thermopower and Mott formula for a Majorana edge state
https://resolver.caltech.edu/CaltechAUTHORS:20131106-131944894
Authors: {'items': [{'id': 'Hou-C-Y', 'name': {'family': 'Hou', 'given': 'Chang-Yu'}}, {'id': 'Shtengel-K', 'name': {'family': 'Shtengel', 'given': 'Kirill'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.88.075304
We study the thermoelectric effect between a conducting lead and a Majorana edge state. In the tunneling limit, we first use the Landauer-Büttiker formalism to derive the Mott formula relating the thermopower and the differential conductance between a conducting lead and a superconductor. When the tunneling takes place between a conducting lead and a Majorana edge state, we show that a nonvanishing thermopower can exist. Combining measurements of the differential conductance and the voltage induced by the temperature difference between the conducting lead and the edge state, the Mott formula provides a unique way to infer the temperature of the Majorana edge state.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0xz56-x2j75Photocurrent response of topological insulator surface states
https://resolver.caltech.edu/CaltechAUTHORS:20131003-112718407
Authors: {'items': [{'id': 'Junck-A', 'name': {'family': 'Junck', 'given': 'Alexandra'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.88.075144
We study the photocurrent response of topological insulator surface states to circularly polarized light for arbitrary oblique incidence. We describe the surface states within a Dirac model, including several perturbations such as hexagonal warping, nonlinear corrections to the mode velocity, and applied magnetic fields. We find that the photogalvanic current is strongly suppressed for the usual orbital coupling, prompting us to include the weaker Zeeman coupling. We find that the helicity-independent photocurrent dominates over the helicity-dependent contributions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/qcdk4-r4y12Strong disorder renormalization group primer and the superfluid–insulator transition
https://resolver.caltech.edu/CaltechAUTHORS:20140228-102011963
Authors: {'items': [{'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Altman-E', 'name': {'family': 'Altman', 'given': 'Ehud'}}]}
Year: 2013
DOI: 10.1016/j.crhy.2013.09.005
This brief review introduces the method and application of real-space renormalization group to strongly disordered quantum systems. The focus is on recent applications of the strong disorder renormalization group to the physics of disordered-boson systems and the superfluid–insulator transition in one dimension. The fact that there is also a well-understood weak disorder theory for this problem allows us to illustrate what aspects of the physics change at strong disorder. In particular, the strong disorder RG analysis suggests that the transitions at weak disorder and strong disorder belong to distinct universality classes, but this question remains under debate and is not fully resolved to date. Further applications of the strong disorder renormalization group to higher-dimensional Bose systems and to bosons coupled to dissipation are also briefly reviewed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vaqc7-v2c62Magneto-Josephson effects and Majorana bound states in quantum wires
https://resolver.caltech.edu/CaltechAUTHORS:20131203-070612581
Authors: {'items': [{'id': 'Pientka-F', 'name': {'family': 'Pientka', 'given': 'Falko'}}, {'id': 'Jiang-Liang', 'name': {'family': 'Jiang', 'given': 'Liang'}, 'orcid': '0000-0002-0000-9342'}, {'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2013
DOI: 10.1088/1367-2630/15/11/115001
A prominent signature of Majorana bound states is the exotic Josephson effects they produce, the classic example being a fractional Josephson current with 4π periodicity in the phase difference across the junction. Recent work established that topological insulator edges support a novel 'magneto-Josephson effect', whereby a dissipationless current exhibits 4π-periodic dependence also on the relative orientation of the Zeeman fields in the two banks of the junction. Here, we explore the magneto-Josephson effect in junctions based on spin–orbit-coupled quantum wires. In contrast to the topological insulator case, the periodicities of the magneto-Josephson effect no longer follow from an exact superconductor–magnetism duality of the Hamiltonian. We employ numerical calculations as well as analytical arguments to identify the domain configurations that display exotic Josephson physics for quantum-wire junctions, and elucidate the characteristic differences with the corresponding setups for topological insulators edges. To provide guidance to experiments, we also estimate the magnitude of the magneto-Josephson effects in realistic parameter regimes, and compare the Majorana-related contribution to the coexisting 2π-periodic effects emerging from non-Majorana states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/93mj0-3af52Boosting Majorana zero modes
https://resolver.caltech.edu/CaltechAUTHORS:20130603-083248608
Authors: {'items': [{'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2013
DOI: 10.1103/PhysRevX.3.041017
One-dimensional topological superconductors are known to host Majorana zero modes at domain walls terminating the topological phase. Their non-Abelian nature allows for processing quantum information by braiding operations that are insensitive to local perturbations, making Majorana zero modes a promising platform for topological quantum computation. Motivated by the ultimate goal of executing quantum-information processing on a finite time scale, we study domain walls moving at a constant velocity. We exploit an effective Lorentz invariance of the Hamiltonian to obtain an exact solution of the associated quasiparticle spectrum and wave functions for arbitrary velocities. Essential features of the solution have a natural interpretation in terms of the familiar relativistic effects of Lorentz contraction and time dilation. We find that the Majorana zero modes remain stable as long as the domain wall moves at subluminal velocities with respect to the effective speed of light of the system. However, the Majorana bound state dissolves into a continuous quasiparticle spectrum after the domain wall propagates at luminal or even superluminal velocities. This relativistic catastrophe implies that there is an upper limit for possible braiding frequencies even in a perfectly clean system with an arbitrarily large topological gap. We also exploit our exact solution to consider domain walls moving past static impurities present in the system.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pd731-3kf37Susceptibility at the superfluid-insulator transition for one-dimensional disordered bosons
https://resolver.caltech.edu/CaltechAUTHORS:20130812-104101196
Authors: {'items': [{'id': 'Iyer-S', 'name': {'family': 'Iyer', 'given': 'Shankar'}}, {'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2013
DOI: 10.1103/PhysRevB.88.220501
A pair of recent Monte Carlo studies have reported evidence for and against a crossover from weak to strong-disorder criticality in the one-dimensional dirty boson problem. The Monte Carlo analyses rely on measurement of two observables: the effective Luttinger parameter K_(eff) and the superfluid susceptibility χ. The former quantity was previously calculated analytically, using the strong-disorder renormalization group (SDRG), by Altman, Kafri, Polkovnikov, and Refael. Here, we use an extension of the SDRG framework to find a non-universal anomalous dimension η_(sd) characterizing the divergence of the susceptibility with system size: χ ~ L^(2-η_(sd)). We show that η_(sd) obeys the hyperscaling relation η_(sd) = 1/2K_(eff). We also identify an important obstacle to measuring this exponent on finite-size systems and comment on the implications for numerics and experiments.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/w0dgm-mst54Semiclassical approach to bound states of a pointlike impurity in a two-dimensional Dirac system
https://resolver.caltech.edu/CaltechAUTHORS:20140402-092139665
Authors: {'items': [{'id': 'Kim-K-W', 'name': {'family': 'Kim', 'given': 'Kun Woo'}}, {'id': 'Pereg-Barnea-T', 'name': {'family': 'Pereg-Barnea', 'given': 'Tami'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2014
DOI: 10.1103/PhysRevB.89.085117
The goal of this paper is to provide an intuitive and useful tool for analyzing the impurity-bound-state problem. We develop a semiclassical approach and apply it to an impurity in two-dimensional systems with parabolic or Dirac-like bands. Our method consists of reducing a higher-dimensional problem into a sum of one-dimensional ones using the two-dimensional Green's functions as a guide. We then analyze the one-dimensional effective systems in the spirit of the wave-function-matching method as in the standard one-dimensional quantum model. We demonstrate our method on two-dimensional models with parabolic and Dirac-like dispersion, with the later specifically relevant to topological insulators.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zptjs-6a812Nonperturbative expression for the transmission through a leaky chiral edge mode
https://resolver.caltech.edu/CaltechAUTHORS:20140417-123053304
Authors: {'items': [{'id': 'Kim-Kun-Woo', 'name': {'family': 'Kim', 'given': 'Kun Woo'}}, {'id': 'Klich-I', 'name': {'family': 'Klich', 'given': 'Israel'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2014
DOI: 10.1103/PhysRevB.89.104204
Chiral edge modes of topological insulators and Hall states exhibit nontrivial behavior of conductance in the presence of impurities or additional channels. We present a simple formula for the conductance through a chiral edge mode coupled to a disordered bulk. For a given coupling matrix between the chiral mode and bulk modes, and a Green's function matrix of bulk modes in real space, the renormalized Green's function of the chiral mode is expressed in closed form as a ratio of determinants. We demonstrate the usage of the formula in two systems: (i) a 1d wire with random on-site impurity potentials for which we found that the disorder averaging is made simpler with the formula, and (ii) a quantum Hall fluid with impurities in the bulk for which the phase picked up by the chiral mode due to the scattering with the impurities can be conveniently estimated.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/sxdyw-0rc60Hilbert-Glass Transition: New Universality of Temperature-Tuned Many-Body Dynamical Quantum Criticality
https://resolver.caltech.edu/CaltechAUTHORS:20140501-160826197
Authors: {'items': [{'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Altman-E', 'name': {'family': 'Altman', 'given': 'Ehud'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'Eugene'}}, {'id': 'Oganesyan-V', 'name': {'family': 'Oganesyan', 'given': 'Vadim'}}]}
Year: 2014
DOI: 10.1103/PhysRevX.4.011052
We study a new class of unconventional critical phenomena that is characterized by singularities only in dynamical quantities and has no thermodynamic signatures. One example of such a transition is the recently proposed many-body localization-delocalization transition, in which transport coefficients vanish at a critical temperature with no singularities in thermodynamic observables. Describing this purely dynamical quantum criticality is technically challenging as understanding the finite-temperature dynamics necessarily requires averaging over a large number of matrix elements between many-body eigenstates. Here, we develop a real-space renormalization group method for excited states that allows us to overcome this challenge in a large class of models. We characterize a specific example: the 1 D disordered transverse-field Ising model with generic interactions. While thermodynamic phase transitions are generally forbidden in this model, using the real-space renormalization group method for excited states we find a finite-temperature dynamical transition between two localized phases. The transition is characterized by nonanalyticities in the low-frequency heat conductivity and in the long-time (dynamic) spin correlation function. The latter is a consequence of an up-down spin symmetry that results in the appearance of an Edwards-Anderson-like order parameter in one of the localized phases.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nxdxf-15g21Disorder-induced Floquet topological insulators in photonic systems
https://resolver.caltech.edu/CaltechAUTHORS:20150109-100216674
Authors: {'items': [{'id': 'Bhattacharjee-P-T', 'name': {'family': 'Bhattacharjee', 'given': 'Paraj T.'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Rechtsman-M-C', 'name': {'family': 'Rechtsman', 'given': 'Mikael C.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2014
DOI: 10.1364/CLEO_QELS.2014.FTh3C.6
We propose the photonic topological Anderson insulator (FTAI), the first realization of the FTAI phase in any physical context (including condensed matter and cold atoms). In this phase, disorder counterintuitively induces a topological transition that breaks Anderson localization and leads to robust transport.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wxejr-tdb19Enhancement of surface photocurrents in topological insulators using magnetic superlattices
https://resolver.caltech.edu/CaltechAUTHORS:20140715-162801579
Authors: {'items': [{'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2014
DOI: 10.48550/arXiv.1403.0010v1
The gapless surface states of topological insulators (TI) can potentially be used to detect and harvest low-frequency infrared light. Nonetheless, it was shown that significant surface photocurrents due to light with frequency below
the bulk gap are rather hard to produce. Here we demonstrate that a periodic
magnetic pattern added to the surface dramatically enhances surface photocurrents in TI's . The ability to produce substantial photocurrents on TI surfaces from mid-range and far-infrared light could be used in photovoltaic applications, as well as for detection of micrometer wavelength radiation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ht0vt-5qb26Current amplification and relaxation in Dirac systems
https://resolver.caltech.edu/CaltechAUTHORS:20140715-163241220
Authors: {'items': [{'id': 'Junck-A', 'name': {'family': 'Junck', 'given': 'Alexandra'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2014
DOI: 10.1103/PhysRevB.90.245110
Recent experiments provide evidence for photocurrent generation in Dirac systems such as topological-insulator surface states and graphene. Within the simplest picture, the magnitude of the photocurrents is governed by the competition between photoexcitation of particle-hole pairs and current relaxation by scattering. Here, we study the relaxation of photocurrents by electron-electron (e−e) collisions, which should dominate in clean systems. We compute the current relaxation rate as a function of the initial energies of the photoexcited carriers and the Fermi energy. For a positive Fermi energy, we find that collisions of a single excited electron with the Fermi sea can substantially increase the current, while for a single excited hole the current initially decreases. Together these processes partially cancel leading to a relative suppression of the relaxation of the total photocurrent carried by an electron-hole pair. We also analyze the limit of many scattering events and find that while e−e collisions initially reduce the current associated with a single hole, the current eventually reverses sign and becomes as large in magnitude as in the electron case. Thus, for photoexcited electron-hole pairs, the current ultimately relaxes to zero. We discuss schemes which may allow one to probe the nontrivial current amplification physics for individual carriers in experiment.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/atxtv-bme27Disorder-induced Floquet Topological Insulators
https://resolver.caltech.edu/CaltechAUTHORS:20140401-114739350
Authors: {'items': [{'id': 'Titum-P', 'name': {'family': 'Titum', 'given': 'Paraj'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Rechtsman-M-C', 'name': {'family': 'Rechtsman', 'given': 'Mikael C.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2015
DOI: 10.1103/PhysRevLett.114.056801
We investigate the possibility of realizing a disorder-induced topological Floquet spectrum in two-dimensional periodically-driven systems. Such a state would be a dynamical realization of the topological Anderson insulator. We establish that a disorder-induced trivial-to-topological transition indeed occurs, and characterize it by computing the disorder averaged Bott index, suitably defined for the time-dependent system. The presence of edge states in the topological state is confirmed by exact numerical time-evolution of wavepackets on the edge of the system. We consider the optimal driving regime for experimentally observing the Floquet-Anderson topological insulator, and discuss its possible realization in photonic lattices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9dt1g-8q098Topological polaritons and excitons in garden-variety systems
https://resolver.caltech.edu/CaltechAUTHORS:20150522-095031056
Authors: {'items': [{'id': 'Bardyn-C-E', 'name': {'family': 'Bardyn', 'given': 'Charles-Edouard'}}, {'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Liew-Timothy-C-H', 'name': {'family': 'Liew', 'given': 'Timothy C. H.'}}]}
Year: 2015
DOI: 10.1103/PhysRevB.91.161413
We present a practical scheme for creating topological polaritons in garden-variety systems based, for example, on zinc-blende semiconductor quantum wells. Our proposal requires a moderate magnetic field and a potential landscape which can be implemented, e.g., via surface acoustic waves or patterning. We identify indirect excitons in double quantum wells as an appealing alternative for topological states in exciton-based systems. Topological polaritons and indirect excitons open a new frontier for topological states in solid-state systems, which can be directly probed and manipulated while offering a system with nonlinear interactions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/me73p-t5s49Experimental realization of a topological Anderson insulator
https://resolver.caltech.edu/CaltechAUTHORS:20160325-092400946
Authors: {'items': [{'id': 'Stützer-S', 'name': {'family': 'Stützer', 'given': 'S.'}}, {'id': 'Rechtsman-M-C', 'name': {'family': 'Rechtsman', 'given': 'M. C.'}}, {'id': 'Titum-P', 'name': {'family': 'Titum', 'given': 'P.'}}, {'id': 'Plotnik-Y', 'name': {'family': 'Plotnik', 'given': 'Y.'}}, {'id': 'Lumer-Y', 'name': {'family': 'Lumer', 'given': 'Y.'}}, {'id': 'Zeuner-J-M', 'name': {'family': 'Zeuner', 'given': 'J. M.'}}, {'id': 'Nolte-S', 'name': {'family': 'Nolte', 'given': 'S.'}, 'orcid': '0000-0002-5393-6326'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'N.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Segev-M', 'name': {'family': 'Segev', 'given': 'M.'}}, {'id': 'Szameit-A', 'name': {'family': 'Szameit', 'given': 'A.'}}]}
Year: 2015
DOI: 10.1364/CLEO_QELS.2015.FTh3D.2
We experimentally demonstrate that disorder can induce a topologically non-trivial phase. We implement this "Topological Anderson Insulator" in arrays of evanescently coupled waveguides and demonstrate its unique features.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/n8gxk-gmf19Shortcuts to non-Abelian braiding
https://resolver.caltech.edu/CaltechAUTHORS:20150504-083749618
Authors: {'items': [{'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Pientka-F', 'name': {'family': 'Pientka', 'given': 'Falko'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2015
DOI: 10.1103/PhysRevB.91.201102
Topological quantum information processing relies on adiabatic braiding of non-Abelian quasiparticles. Performing the braiding operations in finite time introduces transitions out of the ground-state manifold and deviations from the non-Abelian Berry phase. We show that these errors can be eliminated by suitably designed counterdiabatic correction terms in the Hamiltonian. We implement the resulting shortcuts to adiabaticity for simple protocols of non-Abelian braiding and show that the error suppression can be substantial even for approximate realizations of the counterdiabatic terms.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/9kstq-jt331Optimal control of Majorana zero modes
https://resolver.caltech.edu/CaltechAUTHORS:20150604-124203880
Authors: {'items': [{'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Rahmani-A', 'name': {'family': 'Rahmani', 'given': 'Armin'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2015
DOI: 10.1103/PhysRevB.91.201404
Braiding of Majorana zero modes provides a promising platform for quantum information processing, which is topologically protected against errors. Strictly speaking, however, the scheme relies on infinite braiding times as it utilizes the adiabatic limit. Here we show how to minimize nonadiabatic errors for finite braiding times by finding an optimal protocol for the Majorana movement. Interestingly, these protocols are characterized by sharp transitions between Majorana motion at maximal and minimal velocities. We find that these so-called bang-bang protocols can minimize the nonadiabatic transitions of the system by orders of magnitude in comparison with naive protocols.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hgr6w-9j153Topological Polaritons
https://resolver.caltech.edu/CaltechAUTHORS:20140715-152751938
Authors: {'items': [{'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Bardyn-C-E', 'name': {'family': 'Bardyn', 'given': 'Charles-Edouard'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2015
DOI: 10.1103/PhysRevX.5.031001
The interaction between light and matter can give rise to novel topological states. This principle was recently exemplified in Floquet topological insulators, where classical light was used to induce a topological electronic band structure. Here, in contrast, we show that mixing single photons with excitons can result in new topological polaritonic states—or "topolaritons." Taken separately, the underlying photons and excitons are topologically trivial. Combined appropriately, however, they give rise to nontrivial polaritonic bands with chiral edge modes allowing for unidirectional polariton propagation. The main ingredient in our construction is an exciton-photon coupling with a phase that winds in momentum space. We demonstrate how this winding emerges from the finite-momentum mixing between s-type and p-type bands in the electronic system and an applied Zeeman field. We discuss the requirements for obtaining a sizable topological gap in the polariton spectrum and propose practical ways to realize topolaritons in semiconductor quantum wells and monolayer transition metal dichalcogenides.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/tsfef-69f61Holographic treatment of boundary disorder in a topological insulator
https://resolver.caltech.edu/CaltechAUTHORS:20150828-142414208
Authors: {'items': [{'id': 'Kim-Kun-Woo', 'name': {'family': 'Kim', 'given': 'Kun Woo'}}, {'id': 'Mong-R-S-K', 'name': {'family': 'Mong', 'given': 'Roger S. K.'}}, {'id': 'Franz-M', 'name': {'family': 'Franz', 'given': 'Marcel'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2015
DOI: 10.1103/PhysRevB.92.075110
The effect of boundary disorder on electronic systems is particularly interesting for topological phases with surface and edge states. Using exact diagonalization, it has been demonstrated that the surface states of a three-dimensional (3D) topological insulator survive strong surface disorder, and simply get pushed to a clean part of the bulk. Here we explore a method which analytically eliminates the clean bulk and reduces a D-dimensional problem to a Hamiltonian-diagonalization problem within the (D−1)-dimensional disordered boundary. This dramatic reduction in complexity allows the analysis of significantly bigger systems than is possible with exact diagonalization. We use our method to analyze a 2D topological spin-Hall insulator with nonmagnetic and magnetic edge impurities, and we calculate the disorder-induced redistribution of probability density (or local density of states) in the insulating bulk, as well as the transport effects of edge impurities. The analysis reveals how the edge recovers from disorder scattering as the disorder strength increases.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/c4gyy-xcp14Linear magnetoresistance in metals: Guiding center diffusion in a smooth random potential
https://resolver.caltech.edu/CaltechAUTHORS:20151019-160221583
Authors: {'items': [{'id': 'Song-J-C-W', 'name': {'family': 'Song', 'given': 'Justin C. W.'}, 'orcid': '0000-0002-5175-6970'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Lee-P-A', 'name': {'family': 'Lee', 'given': 'Patrick A.'}}]}
Year: 2015
DOI: 10.1103/PhysRevB.92.180204
We predict that guiding center (GC) diffusion yields a linear and nonsaturating (transverse) magnetoresistance in 3D metals. Our theory is semiclassical and applies in the regime where the transport time is much greater than the cyclotron period and for weak disorder potentials which are slowly varying on a length scale much greater than the cyclotron radius. Under these conditions, orbits with small momenta along magnetic field B are squeezed and dominate the transverse conductivity. When disorder potentials are stronger than the Debye frequency, linear magnetoresistance is predicted to survive up to room temperature and beyond. We argue that magnetoresistance from GC diffusion explains the recently observed giant linear magnetoresistance in 3D Dirac materials.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/69qv1-8qf24Controlled Population of Floquet-Bloch States via Coupling to Bose and Fermi Baths
https://resolver.caltech.edu/CaltechAUTHORS:20160121-131612700
Authors: {'items': [{'id': 'Seetharam-K-I', 'name': {'family': 'Seetharam', 'given': 'Karthik I.'}}, {'id': 'Bardyn-C-E', 'name': {'family': 'Bardyn', 'given': 'Charles-Edouard'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Rudner-M-S', 'name': {'family': 'Rudner', 'given': 'Mark S.'}, 'orcid': '0000-0002-5150-6234'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2015
DOI: 10.1103/PhysRevX.5.041050
External driving is emerging as a promising tool for exploring new phases in quantum systems. The intrinsically nonequilibrium states that result, however, are challenging to describe and control. We study the steady states of a periodically driven one-dimensional electronic system, including the effects of radiative recombination, electron-phonon interactions, and the coupling to an external fermionic reservoir. Using a kinetic equation for the populations of the Floquet eigenstates, we show that the steady-state distribution can be controlled using the momentum and energy relaxation pathways provided by the coupling to phonon and Fermi reservoirs. In order to utilize the latter, we propose to couple the system and reservoir via an energy filter which suppresses photon-assisted tunneling. Importantly, coupling to these reservoirs yields a steady state resembling a band insulator in the Floquet basis. The system exhibits incompressible behavior, while hosting a small density of excitations. We discuss transport signatures and describe the regimes where insulating behavior is obtained. Our results give promise for realizing Floquet topological insulators.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nz7de-ndy45Chiral Bogoliubov excitations in nonlinear bosonic systems
https://resolver.caltech.edu/CaltechAUTHORS:20150427-125004319
Authors: {'items': [{'id': 'Bardyn-C-E', 'name': {'family': 'Bardyn', 'given': 'Charles-Edouard'}}, {'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Liew-T-C-H', 'name': {'family': 'Liew', 'given': 'Tomothy C. H.'}}]}
Year: 2016
DOI: 10.1103/PhysRevB.93.020502
We present a versatile scheme for creating topological Bogoliubov excitations in weakly interacting bosonic systems. Our proposal relies on a background stationary field that consists of a Kagome vortex lattice, which breaks time-reversal symmetry and induces a periodic potential for Bogoliubov excitations. In analogy to the Haldane model, no external magnetic field or net flux is required. We construct a generic model based on the two-dimensional (2D) nonlinear Schrödinger equation and demonstrate the emergence of topological gaps crossed by chiral Bogoliubov edge modes. Our scheme can be realized in a wide variety of physical systems ranging from nonlinear optical systems to exciton-polariton condensates.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/hswq2-ff384Topological polaritons in a quantum spin Hall cavity
https://resolver.caltech.edu/CaltechAUTHORS:20160525-140247002
Authors: {'items': [{'id': 'Janot-A', 'name': {'family': 'Janot', 'given': 'Alexander'}}, {'id': 'Rosenow-B', 'name': {'family': 'Rosenow', 'given': 'Bernd'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2016
DOI: 10.1103/PhysRevB.93.161111
We study the topological structure of matter-light excitations, so-called polaritons, in a quantum spin Hall insulator coupled to photonic cavity modes. We identify a topological invariant in the presence of time reversal (TR) symmetry, and demonstrate the existence of a TR-invariant topological phase. We find protected helical edge states with energies below the lower polariton branch and characteristic uncoupled excitonic states, both detectable by optical techniques. Applying a Zeeman field allows us to relate the topological index to the double coverage of the Bloch sphere by the polaritonic pseudospin.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/h8wn7-tpj59Anomalous Floquet-Anderson Insulator as a Nonadiabatic Quantized Charge Pump
https://resolver.caltech.edu/CaltechAUTHORS:20150824-133019180
Authors: {'items': [{'id': 'Titum-P', 'name': {'family': 'Titum', 'given': 'Paraj'}}, {'id': 'Berg-E', 'name': {'family': 'Berg', 'given': 'Erez'}}, {'id': 'Rudner-M-S', 'name': {'family': 'Rudner', 'given': 'Mark S.'}, 'orcid': '0000-0002-5150-6234'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}]}
Year: 2016
DOI: 10.1103/PhysRevX.6.021013
We show that two-dimensional periodically driven quantum systems with spatial disorder admit a unique topological phase, which we call the anomalous Floquet-Anderson insulator (AFAI). The AFAI is characterized by a quasienergy spectrum featuring chiral edge modes coexisting with a fully localized bulk. Such a spectrum is impossible for a time-independent, local Hamiltonian. These unique characteristics of the AFAI give rise to a new topologically protected nonequilibrium transport phenomenon: quantized, yet nonadiabatic, charge pumping. We identify the topological invariants that distinguish the AFAI from a trivial, fully localized phase, and show that the two phases are separated by a phase transition.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/vk3ms-jsb05Universal Geometric Path to a Robust Majorana Magic Gate
https://resolver.caltech.edu/CaltechAUTHORS:20160602-064512689
Authors: {'items': [{'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Freedman-M-H', 'name': {'family': 'Freedman', 'given': 'Michael H.'}}]}
Year: 2016
DOI: 10.1103/PhysRevX.6.031019
A universal quantum computer requires a full set of basic quantum gates. With Majorana bound states one can form all necessary quantum gates in a topologically protected way, bar one. In this paper, we present a scheme that achieves the missing, so-called, π/8 magic phase gate without the need of fine-tuning for distinct physical realizations. The scheme is based on the manipulation of geometric phases described by a universal protocol and converges exponentially with the number of steps in the geometric path. Furthermore, our magic gate proposal relies on the most basic hardware previously suggested for topologically protected gates, and can be extended to an any-phase gate, where π/8 is substituted by any α.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4xs1d-mj985Dynamical many-body localization in an integrable model
https://resolver.caltech.edu/CaltechAUTHORS:20160811-105244924
Authors: {'items': [{'id': 'Keser-A-C', 'name': {'family': 'Keser', 'given': 'Aydin Cem'}}, {'id': 'Ganeshan-S', 'name': {'family': 'Ganeshan', 'given': 'Sriram'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Galitski-V', 'name': {'family': 'Galitski', 'given': 'Victor'}}]}
Year: 2016
DOI: 10.1103/PhysRevB.94.085120
We investigate dynamical many-body localization and delocalization in an integrable system of periodically-kicked, interacting linear rotors. The linear-in-momentum Hamiltonian makes the Floquet evolution operator analytically tractable for arbitrary interactions. One of the hallmarks of this model is that depending on certain parameters, it manifests both localization and delocalization in momentum space. We present a set of "emergent" integrals of motion, which can serve as a fundamental diagnostic of dynamical localization in the interacting case. We also propose an experimental scheme, involving voltage-biased Josephson junctions, to realize such many-body kicked models.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y46xm-qw110Localization transition in one dimension using Wegner flow equations
https://resolver.caltech.edu/CaltechAUTHORS:20160928-115939815
Authors: {'items': [{'id': 'Quito-V-L', 'name': {'family': 'Quito', 'given': 'Victor L.'}}, {'id': 'Titum-P', 'name': {'family': 'Titum', 'given': 'Paraj'}}, {'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2016
DOI: 10.1103/PhysRevB.94.104202
The flow-equation method was proposed by Wegner as a technique for studying interacting systems in one dimension. Here, we apply this method to a disordered one-dimensional model with power-law decaying hoppings. This model presents a transition as function of the decaying exponent α. We derive the flow equations and the evolution of single-particle operators. The flow equation reveals the delocalized nature of the states for α<12. Additionally, in the regime α>12, we present a strong-bond renormalization group structure based on iterating the three-site clusters, where we solve the flow equations perturbatively. This renormalization group approach allows us to probe the critical point (α=1). This method correctly reproduces the critical level-spacing statistics and the fractal dimensionality of the eigenfunctions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/xmyk5-8he93Dynamical Cooper pairing in nonequilibrium electron-phonon systems
https://resolver.caltech.edu/CaltechAUTHORS:20161208-153127646
Authors: {'items': [{'id': 'Knap-M', 'name': {'family': 'Knap', 'given': 'Michael'}}, {'id': 'Babadi-M', 'name': {'family': 'Babadi', 'given': 'Mehrtash'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Martin-I', 'name': {'family': 'Martin', 'given': 'Ivar'}, 'orcid': '0000-0002-2010-6449'}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'Eugene'}}]}
Year: 2016
DOI: 10.1103/PhysRevB.94.214504
We analyze Cooper pairing instabilities in strongly driven electron-phonon systems. The light-induced nonequilibrium state of phonons results in a simultaneous increase of the superconducting coupling constant and the electron scattering. We demonstrate that the competition between these effects leads to an enhanced superconducting transition temperature in a broad range of parameters. Our results may explain the observed transient enhancement of superconductivity in several classes of materials upon irradiation with high intensity pulses of terahertz light, and may pave new ways for engineering high-temperature light-induced superconducting states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/g2r52-3sr57Remnant Geometric Hall Response in a Quantum Quench
https://resolver.caltech.edu/CaltechAUTHORS:20160714-082247839
Authors: {'items': [{'id': 'Wilson-J-H', 'name': {'family': 'Wilson', 'given': 'Justin H.'}, 'orcid': '0000-0001-6903-0417'}, {'id': 'Song-Justin-C-W', 'name': {'family': 'Song', 'given': 'Justin C. W.'}, 'orcid': '0000-0002-5175-6970'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2016
DOI: 10.1103/PhysRevLett.117.235302
Out-of-equilibrium systems can host phenomena that transcend the usual restrictions of equilibrium systems. Here we unveil how out-of-equilibrium states, prepared via a quantum quench, can exhibit a non-zero Hall-type response that persists at long times, and even when the instantaneous Hamiltonian is time reversal symmetric; both these features starkly contrast with equilibrium Hall currents. Interestingly, the persistent Hall effect arises from processes beyond those captured by linear response, and is a signature of the novel dynamics in out-of-equilibrium systems. We propose quenches in two-band Dirac systems as natural venues to realize persistent Hall currents, which exist when either mirror or time-reversal symmetry are broken (before or after the quench). Its long time persistence, as well as sensitivity to symmetry breaking, allow it to be used as a sensitive diagnostic of the complex out-equilibrium dynamics readily controlled and probed in cold-atomic optical lattice experiments.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p4sed-rd839Quantum information sharing between topologically distinct platforms
https://resolver.caltech.edu/CaltechAUTHORS:20160510-083323766
Authors: {'items': [{'id': 'Hou-Chang-Yu', 'name': {'family': 'Hou', 'given': 'Chang-Yu'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Shtengel-K', 'name': {'family': 'Shtengel', 'given': 'Kirill'}}]}
Year: 2016
DOI: 10.1103/PhysRevB.94.235113
Can topological quantum entanglement between anyons in one topological medium "stray" into a different, topologically distinct medium? In other words, can quantum information encoded nonlocally in the combined state of non-Abelian anyons be shared between two distinct topological media? For one-dimensional topological superconductors with Majorana bound states at the end of system, the quantum information store in those Majorana bound states can be transfered by directly coupling nearby Majorana bound states. However, coupling of two one-dimensional Majorana states will produce a gap, indicating that distinct topological regions of one-dimensional wires unite into a single topological region through the information transfer process. In this paper, we consider a setup with two two-dimensional p -wave superconductors of opposite chirality adjacent to each other. Even two comoving chiral modes at the domain wall between them cannot be gapped through interactions; we demonstrate that information encoded in the fermionic parity of two Majorana zero modes, originally within the same superconducting domain, can be shared between the domains or moved entirely from one domain to another provided that vortices can tunnel between them in a controlled fashion.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ybbsj-50g20Photocurrents in Weyl semimetals
https://resolver.caltech.edu/CaltechAUTHORS:20170119-140307907
Authors: {'items': [{'id': 'Chan-Ching-Kit', 'name': {'family': 'Chan', 'given': 'Ching-Kit'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Lee-P-A', 'name': {'family': 'Lee', 'given': 'Patrick A.'}}]}
Year: 2017
DOI: 10.1103/PhysRevB.95.041104
The generation of photocurrent in an ideal two-dimensional Dirac spectrum is symmetry forbidden. In sharp contrast, we show that three-dimensional Weyl semimetals can generically support significant photocurrents due to the combination of inversion symmetry breaking and finite tilts of the Weyl spectra. Symmetry properties, chirality relations, and various dependencies of this photovoltaic effect on the system and the light source are explored in detail. Our results suggest that noncentrosymmetric Weyl materials can be advantageously applied to room temperature detections of mid- and far-infrared radiations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/j4sad-b2d22The theory of parametrically amplified electron-phonon superconductivity
https://resolver.caltech.edu/CaltechAUTHORS:20170619-085401037
Authors: {'items': [{'id': 'Babadi-M', 'name': {'family': 'Babadi', 'given': 'Mehrtash'}}, {'id': 'Knap-M', 'name': {'family': 'Knap', 'given': 'Michael'}}, {'id': 'Martin-I', 'name': {'family': 'Martin', 'given': 'Ivar'}, 'orcid': '0000-0002-2010-6449'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Demler-E', 'name': {'family': 'Demler', 'given': 'Eugene'}}]}
Year: 2017
DOI: 10.1103/PhysRevB.96.014512
Ultrafast optical manipulation of ordered phases in strongly correlated materials is a topic of significant theoretical, experimental, and technological interest. Inspired by a recent experiment on light-induced superconductivity in fullerenes [M. Mitrano et al., Nature (London) 530, 461 (2016)], we develop a comprehensive theory of light-induced superconductivity in driven electron-phonon systems with lattice nonlinearities. In analogy with the operation of parametric amplifiers, we show how the interplay between the external drive and lattice nonlinearities lead to significantly enhanced effective electron-phonon couplings. We provide a detailed and unbiased study of the nonequilibrium dynamics of the driven system using the real-time Green's function technique. To this end, we develop a Floquet generalization of the Migdal-Eliashberg theory and derive a numerically tractable set of quantum Floquet-Boltzmann kinetic equations for the coupled electron-phonon system. We study the role of parametric phonon generation and electronic heating in destroying the transient superconducting state. Finally, we predict the transient formation of electronic Floquet bands in time- and angle-resolved photoemission spectroscopy experiments as a consequence of the proposed mechanism.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/c9kdn-2g503Driving induced many-body localization
https://resolver.caltech.edu/CaltechAUTHORS:20170719-094811145
Authors: {'items': [{'id': 'Bairey-E', 'name': {'family': 'Bairey', 'given': 'Eyal'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}]}
Year: 2017
DOI: 10.1103/PhysRevB.96.020201
Subjecting a many-body localized system to a time-periodic drive generically leads to delocalization and a transition to ergodic behavior if the drive is sufficiently strong or of sufficiently low frequency. Here we show that a specific drive can have an opposite effect, taking a static delocalized system into the many-body localized phase. We demonstrate this effect using a one-dimensional system of interacting hard-core bosons subject to an oscillating linear potential. The system is weakly disordered, and is ergodic absent the driving. The time-periodic linear potential leads to a suppression of the effective static hopping amplitude, increasing the relative strengths of disorder and interactions. Using numerical simulations, we find a transition into the many-body localized phase above a critical driving frequency and in a range of driving amplitudes. Our findings highlight the potential of driving schemes exploiting the coherent destruction of tunneling for engineering long-lived Floquet phases.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/62wrm-8p222Disorder induced transitions in resonantly driven Floquet Topological Insulators
https://resolver.caltech.edu/CaltechAUTHORS:20170619-091103005
Authors: {'items': [{'id': 'Titum-P', 'name': {'family': 'Titum', 'given': 'Paraj'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2017
DOI: 10.1103/PhysRevB.96.054207
We investigate the effects of disorder in Floquet topological insulators (FTIs) occurring in semiconductor quantum wells. Such FTIs are induced by resonantly driving a transition between the valence and conduction bands. We show that when disorder is added, the topological nature of such FTIs persists as long as there is a mobility gap at the resonant quasienergy. For strong enough disorder, this gap closes and all the states become localized as the system undergoes a transition to a trivial insulator. Interestingly, the effects of disorder are not necessarily adverse: we show that in the same quantum well, disorder can also induce a transition from a trivial to a topological system, thereby establishing a Floquet topological Anderson insulator (FTAI). We identify the conditions on the driving field necessary for observing such a transition.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0g9ar-w4v18Fixed Points of Wegner-Wilson Flows and Many-Body Localization
https://resolver.caltech.edu/CaltechAUTHORS:20170817-073043882
Authors: {'items': [{'id': 'Pekker-D', 'name': {'family': 'Pekker', 'given': 'David'}}, {'id': 'Clark-B-K', 'name': {'family': 'Clark', 'given': 'Bryan K.'}}, {'id': 'Oganesyan-V', 'name': {'family': 'Oganesyan', 'given': 'Vadim'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2017
DOI: 10.1103/PhysRevLett.119.075701
Many-body localization (MBL) is a phase of matter that is characterized by the absence of thermalization. Dynamical generation of a large number of local quantum numbers has been identified as one key characteristic of this phase, quite possibly the microscopic mechanism of breakdown of thermalization and the phase transition itself. We formulate a robust algorithm, based on Wegner-Wilson flow (WWF) renormalization, for computing these conserved quantities and their interactions. We present evidence for the existence of distinct fixed point distributions of the latter: a Gaussian white-noise-like distribution in the ergodic phase, a 1/f law inside the MBL phase, and scale-free distributions in the transition regime.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/w40ht-ny583Stable Unitary Integrators for the Numerical Implementation of Continuous Unitary Transformations
https://resolver.caltech.edu/CaltechAUTHORS:20171004-144154017
Authors: {'items': [{'id': 'Savitz-S', 'name': {'family': 'Savitz', 'given': 'Samuel'}, 'orcid': '0000-0003-2112-3758'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2017
DOI: 10.1103/PhysRevB.96.115129
The technique of continuous unitary transformations has recently been used to provide physical insight into a diverse array of quantum mechanical systems. However, the question of how to best numerically implement the flow equations has received little attention. The most immediately apparent approach, using standard Runge-Kutta numerical integration algorithms, suffers from both severe inefficiency due to stiffness and the loss of unitarity. After reviewing the formalism of continuous unitary transformations and Wegner's original choice for the infinitesimal generator of the flow, we present a number of approaches to resolving these issues including a choice of generator which induces what we call the "uniform tangent decay flow" and three numerical integrators specifically designed to perform continuous unitary transformations efficiently while preserving the unitarity of flow. We conclude by applying one of the flow algorithms to a simple calculation that visually demonstrates the many-body localization transition.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/p3b83-x3n24Topological frequency conversion in strongly driven quantum systems
https://resolver.caltech.edu/CaltechAUTHORS:20171011-110835402
Authors: {'items': [{'id': 'Martin-I', 'name': {'family': 'Martin', 'given': 'Ivar'}, 'orcid': '0000-0002-2010-6449'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Halperin-B-I', 'name': {'family': 'Halperin', 'given': 'Bertrand'}, 'orcid': '0000-0002-6999-1039'}]}
Year: 2017
DOI: 10.1103/PhysRevX.7.041008
When a physical system is subjected to a strong external multifrequency drive, its dynamics can be conveniently represented in the multidimensional Floquet lattice. The number of Floquet lattice dimensions equals the number of irrationally-related drive frequencies, and the evolution occurs in response to a built-in effective "electric" field, whose components are proportional to the corresponding drive frequencies. The mapping allows us to engineer and study temporal analogs of many real-space phenomena. Here, we focus on the specific example of a two-level system under a two-frequency drive that induces topologically nontrivial band structure in the 2D Floquet space. The observable consequence of such a construction is the quantized pumping of energy between the sources with frequencies ω_1 and ω_2. When the system is initialized into a Floquet band with the Chern number C, the pumping occurs at a rate P_(12)=−P_(21)=(C/2π)ℏω_1ω_2, an exact counterpart of the transverse current in a conventional topological insulator.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/89tex-ext79Quantized Magnetization Density in Periodically Driven Systems
https://resolver.caltech.edu/CaltechAUTHORS:20171101-122220832
Authors: {'items': [{'id': 'Nathan-F', 'name': {'family': 'Nathan', 'given': 'Frederik'}}, {'id': 'Rudner-M-S', 'name': {'family': 'Rudner', 'given': 'Mark S.'}, 'orcid': '0000-0002-5150-6234'}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Berg-E', 'name': {'family': 'Berg', 'given': 'Erez'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2017
DOI: 10.1103/PhysRevLett.119.186801
We study micromotion in two-dimensional periodically driven systems in which all bulk Floquet eigenstates are localized by disorder. We show that this micromotion gives rise to a quantized time-averaged orbital magnetization density in any region completely filled with fermions. The quantization of magnetization density has a topological origin, and reveals the physical nature of the new phase identified in P. Titum, E. Berg, M. S. Rudner, G. Refael, and N. H. Lindner [Phys. Rev. X 6, 021013 (2016)]. We thus establish that the topological index of this phase can be accessed directly in bulk measurements, and propose an experimental protocol to do so using interferometry in cold-atom-based realizations.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/wcyh5-hb048Absence of thermalization in finite isolated interacting Floquet systems
https://resolver.caltech.edu/CaltechAUTHORS:20180130-143240205
Authors: {'items': [{'id': 'Seetharam-K-I', 'name': {'family': 'Seetharam', 'given': 'Karthik'}}, {'id': 'Titum-P', 'name': {'family': 'Titum', 'given': 'Paraj'}}, {'id': 'Kolodrubetz-M', 'name': {'family': 'Kolodrubetz', 'given': 'Michael'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2018
DOI: 10.1103/PhysRevB.97.014311
Conventional wisdom suggests that the long-time behavior of isolated interacting periodically driven (Floquet) systems is a featureless maximal-entropy state characterized by an infinite temperature. Efforts to thwart this uninteresting fixed point include adding sufficient disorder to realize a Floquet many-body localized phase or working in a narrow region of drive frequencies to achieve glassy nonthermal behavior at long time. Here we show that in clean systems the Floquet eigenstates can exhibit nonthermal behavior due to finite system size. We consider a one-dimensional system of spinless fermions with nearest-neighbor interactions where the interaction term is driven. Interestingly, even with no static component of the interaction, the quasienergy spectrum contains gaps and a significant fraction of the Floquet eigenstates, at all quasienergies, have nonthermal average doublon densities. We show that this nonthermal behavior arises due to emergent integrability at large interaction strength and discuss how the integrability breaks down with power-law dependence on system size.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/6e4ky-rxt58Quantum dynamics of thermalizing systems
https://resolver.caltech.edu/CaltechAUTHORS:20170925-082950649
Authors: {'items': [{'id': 'White-C-D', 'name': {'family': 'White', 'given': 'Christopher David'}}, {'id': 'Zaletel-M-P', 'name': {'family': 'Zaletel', 'given': 'Michael'}}, {'id': 'Mong-Roger-S-K', 'name': {'family': 'Mong', 'given': 'Roger S. K.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2018
DOI: 10.1103/PhysRevB.97.035127
We introduce a method "DMT" for approximating density operators of 1D systems that, when combined with a standard framework for time evolution (TEBD), makes possible simulation of the dynamics of strongly thermalizing systems to arbitrary times. We demonstrate that the method performs well for both near-equilibrium initial states (Gibbs states with spatially varying temperatures) and far-from-equilibrium initial states, including quenches across phase transitions and pure states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/7r9qj-aph20Setting Boundaries with Memory: Generation of Topological Boundary States in Floquet-Induced Synthetic Crystals
https://resolver.caltech.edu/CaltechAUTHORS:20171004-143507726
Authors: {'items': [{'id': 'Baum-Y', 'name': {'family': 'Baum', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2018
DOI: 10.1103/PhysRevLett.120.106402
When a d-dimensional quantum system is subjected to a periodic drive, it may be treated as a (d+1)-dimensional system, where the extra dimension is a synthetic one. This approach, however, affords only a limited level of control of the effective potential along the synthetic direction. In this work, we introduce a new mean for controlling the Floquet synthetic dimension. We show that arbitrary potentials, as well as edges in the synthetic dimension, could be introduced using a memory component in the system's dynamics. We demonstrate this principle by exploring topological edge states propagating normal to synthetic dimensions. Such systems may act as an optical isolator which allows the transmission of light in a directional way. Also, we suggest an experimental realization of the memory effect in spins coupled to nanofabricated Weyl semimetal surface states.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/202q5-4cv91Topological energy conversion through the bulk or the boundary of driven systems
https://resolver.caltech.edu/CaltechAUTHORS:20180416-135742666
Authors: {'items': [{'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2018
DOI: 10.1103/PhysRevB.97.134303
Combining physical and synthetic dimensions allows a controllable realization and manipulation of high-dimensional topological states. In our work, we introduce two quasiperiodically driven one-dimensional systems which enable tunable topological energy conversion between different driving sources. Using three drives, we realize a four-dimensional quantum Hall state which allows energy conversion between two of the drives within the bulk of the one-dimensional system. With only two drives, we achieve energy conversion between the two at the edge of the chain. Both effects are a manifestation of the effective axion electrodynamics in a three-dimensional time-reversal-invariant topological insulator. Furthermore, we explore the effects of disorder and commensurability of the driving frequencies, and show the phenomena are robust. We propose two experimental platforms, based on semiconductor heterostructures and ultracold atoms in optical lattices, in order to observe the topological energy conversion.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/y0jkg-81520Interacting adiabatic quantum motor
https://resolver.caltech.edu/CaltechAUTHORS:20180509-110549288
Authors: {'items': [{'id': 'Bruch-A', 'name': {'family': 'Bruch', 'given': 'Anton'}}, {'id': 'Kusminskiy-S-V', 'name': {'family': 'Kusminskiy', 'given': 'Silvia Viola'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}]}
Year: 2018
DOI: 10.1103/PhysRevB.97.195411
We present a field-theoretic treatment of an adiabatic quantum motor. We explicitly discuss a motor called the Thouless motor which is based on a Thouless pump operating in reverse. When a sliding periodic potential is considered to be the motor degree of freedom, a bias voltage applied to the electron channel sets the motor in motion. We investigate a Thouless motor whose electron channel is modeled as a Luttinger liquid. Interactions increase the gap opened by the periodic potential. For an infinite Luttinger liquid the coupling-induced friction is enhanced by electron-electron interactions. When the Luttinger liquid is ultimately coupled to Fermi liquid reservoirs, the dissipation reduces to its value for a noninteracting electron system for a constant motor velocity. Our results can also be applied to a motor based on a nanomagnet coupled to a quantum spin Hall edge.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8epmr-22q41Quantized transport and steady states of Floquet topological insulators
https://resolver.caltech.edu/CaltechAUTHORS:20180606-094237198
Authors: {'items': [{'id': 'Esin-I', 'name': {'family': 'Esin', 'given': 'Ilya'}}, {'id': 'Rudner-M-S', 'name': {'family': 'Rudner', 'given': 'Mark S.'}, 'orcid': '0000-0002-5150-6234'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}]}
Year: 2018
DOI: 10.1103/PhysRevB.97.245401
Robust electronic edge or surface modes play key roles in the fascinating quantized responses exhibited by topological materials. Even in trivial materials, topological bands and edge states can be induced dynamically by a time-periodic drive. Such Floquet topological insulators (FTIs) inherently exist out of equilibrium; the extent to which they can host quantized transport, which depends on the steady-state population of their dynamically induced edge states, remains a crucial question. In this work, we obtain the steady states of two-dimensional FTIs in the presence of the natural dissipation mechanisms present in solid state systems. We give conditions under which the steady-state distribution resembles that of a topological insulator in the Floquet basis. In this state, the distribution in the Floquet edge modes exhibits a sharp feature akin to a Fermi level, while the bulk hosts a small density of excitations. We determine the regimes where topological edge-state transport persists and can be observed in FTIs.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/t6w35-t2v44Do the surface Fermi arcs in Weyl semimetals survive disorder?
https://resolver.caltech.edu/CaltechAUTHORS:20180607-103545257
Authors: {'items': [{'id': 'Wilson-J-H', 'name': {'family': 'Wilson', 'given': 'Justin H.'}, 'orcid': '0000-0001-6903-0417'}, {'id': 'Pixley-J-H', 'name': {'family': 'Pixley', 'given': 'J. H.'}}, {'id': 'Huse-D-A', 'name': {'family': 'Huse', 'given': 'David A.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Sarma-S-D', 'name': {'family': 'Sarma', 'given': 'S. Das'}}]}
Year: 2018
DOI: 10.1103/PhysRevB.97.235108
We theoretically study the topological robustness of the surface physics induced by Weyl Fermi-arc surface states in the presence of short-ranged quenched disorder and surface-bulk hybridization. This is investigated with numerically exact calculations on a lattice model exhibiting Weyl Fermi arcs. We find that the Fermi-arc surface states, in addition to having a finite lifetime from disorder broadening, hybridize with nonperturbative bulk rare states making them no longer bound to the surface (i.e., they lose their purely surface spectral character). Thus, we provide strong numerical evidence that the Weyl Fermi arcs are not topologically protected from disorder. Nonetheless, the surface chiral velocity is robust and survives in the presence of strong disorder, persisting all the way to the Anderson-localized phase by forming localized current loops that live within the localization length of the surface. Thus, the Weyl semimetal is not topologically robust to the presence of disorder, but the surface chiral velocity is.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/gx2px-hbm14Learning phase transitions from dynamics
https://resolver.caltech.edu/CaltechAUTHORS:20180723-093013664
Authors: {'items': [{'id': 'van-Nieuwenburg-E-P-L', 'name': {'family': 'van Nieuwenburg', 'given': 'Evert'}, 'orcid': '0000-0003-0323-0031'}, {'id': 'Bairey-E', 'name': {'family': 'Bairey', 'given': 'Eyal'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2018
DOI: 10.1103/PhysRevB.98.060301
We propose the use of recurrent neural networks for classifying phases of matter based on the dynamics of experimentally accessible observables. We demonstrate this approach by training recurrent networks on the magnetization traces of two distinct models of one-dimensional disordered and interacting spin chains. The obtained phase diagram for a well-studied model of the many-body localization transition shows excellent agreement with previously known results obtained from time-independent entanglement spectra. For a periodically driven model featuring an inherently dynamical time-crystalline phase, the phase diagram that our network traces coincides with an order parameter for its expected phases.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/344hq-eg740Berry electrodynamics: Anomalous drift and pumping from a time-dependent Berry connection
https://resolver.caltech.edu/CaltechAUTHORS:20180521-092304073
Authors: {'items': [{'id': 'Chaudhary-Swati', 'name': {'family': 'Chaudhary', 'given': 'Swati'}}, {'id': 'Endres-M', 'name': {'family': 'Endres', 'given': 'Manuel'}, 'orcid': '0000-0002-4461-224X'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2018
DOI: 10.1103/PhysRevB.98.064310
The Berry curvature of a Bloch band can be interpreted as a local magnetic field in reciprocal space. This analogy can be extended by defining an electric field analog in reciprocal space which arises from the time-dependent Berry connection. We explore the term in the semiclassical equation of motion that gives rise to this phenomenon, and show that it can lead to anomalous drift in wave-packet motion. A similar effect arises from changes in the band population due to periodic driving, where the resulting drift depends on the nature of the drive and can be expressed in terms of a shift vector. Finally, these effects can be combined to build a pump with a net anomalous drift during a cyclic evolution in momentum space.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/bnmf7-v2737From dynamical localization to bunching in interacting Floquet systems
https://resolver.caltech.edu/CaltechAUTHORS:20180620-195305259
Authors: {'items': [{'id': 'Baum-Y', 'name': {'family': 'Baum', 'given': 'Yuval'}}, {'id': 'van-Nieuwenburg-E-P-L', 'name': {'family': 'van Nieuwenburg', 'given': 'Evert P. L.'}, 'orcid': '0000-0003-0323-0031'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2018
DOI: 10.21468/SciPostPhys.5.2.017
We show that a quantum many-body system may be controlled by means of Floquet engineering, i.e., their properties may be controlled and manipulated by employing periodic driving. We present a concrete driving scheme that allows control over the nature of mobile units and the amount of diffusion in generic many-body systems. We demonstrate these ideas for the Fermi-Hubbard model, where the drive renders doubly occupied sites (doublons) the mobile excitations in the system. In particular, we show that the amount of diffusion in the system and the level of fermion-pairing may be controlled and understood solely in terms of the doublon dynamics. We find that under certain circumstances the diffusion in the system may be eliminated completely. We conclude our work by generalizing these ideas to generic many-body systems.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/4x7fp-4sb88Time-quasiperiodic topological superconductors with Majorana multiplexing
https://resolver.caltech.edu/CaltechAUTHORS:20180521-093207551
Authors: {'items': [{'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2018
DOI: 10.1103/physrevb.98.220509
Time-quasiperiodic Majoranas are generalizations of Floquet Majoranas in time-quasiperiodic superconducting systems. We show that in a system driven at d mutually irrational frequencies, there are up to 2^d types of such Majoranas, coexisting despite spatial overlap and lack of time-translational invariance. Although the quasienergy spectrum is dense in such systems, the time-quasiperiodic Majoranas can be stable and robust against resonances due to localization in periodic-drive-induced synthetic dimensions. This is demonstrated in a time-quasiperiodic Kitaev chain driven at two frequencies. We further relate the existence of multiple Majoranas in a time-quasiperiodic system to the time-quasicrystal phase introduced recently. These time-quasiperiodic Majoranas open a possibility for braiding which will be pursued in the future.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5hdpy-p3298Steady state of interacting Floquet insulators
https://resolver.caltech.edu/CaltechAUTHORS:20180710-135957911
Authors: {'items': [{'id': 'Seetharam-K-I', 'name': {'family': 'Seetharam', 'given': 'Karthik I.'}}, {'id': 'Bardyn-C-E', 'name': {'family': 'Bardyn', 'given': 'Charles-Edouard'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}, {'id': 'Rudner-M-S', 'name': {'family': 'Rudner', 'given': 'Mark S.'}, 'orcid': '0000-0002-5150-6234'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2019
DOI: 10.1103/PhysRevB.99.014307
Floquet engineering offers tantalizing opportunities for controlling the dynamics of quantum many-body systems and realizing new nonequilibrium phases of matter. However, this approach faces a major challenge: generic interacting Floquet systems absorb energy from the drive, leading to uncontrolled heating which washes away the sought-after behavior. How to achieve and control a nontrivial nonequilibrium steady state is therefore of crucial importance. In this work, we study the dynamics of an interacting one-dimensional periodically driven electronic system coupled to a phonon heat bath. Using the Floquet-Boltzmann equation (FBE) we show that the electronic populations of the Floquet eigenstates can be controlled by the dissipation. We find the regime in which the steady state features an insulator-like filling of the Floquet bands, with a low density of additional excitations. Furthermore, we develop a simple rate equation model for the steady state excitation density that captures the behavior obtained from the numerical solution of the FBE over a wide range of parameters.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/dxbnv-cs375Quantum engine based on many-body localization
https://resolver.caltech.edu/CaltechAUTHORS:20171004-143754557
Authors: {'items': [{'id': 'Yunger-Halpern-N', 'name': {'family': 'Yunger Halpern', 'given': 'Nicole'}, 'orcid': '0000-0001-8670-6212'}, {'id': 'White-C-D', 'name': {'family': 'White', 'given': 'Christopher David'}}, {'id': 'Gopalakrishnan-S', 'name': {'family': 'Gopalakrishnan', 'given': 'Sarang'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2019
DOI: 10.1103/PhysRevB.99.024203
Many-body-localized (MBL) systems do not thermalize under their intrinsic dynamics. The athermality of MBL, we propose, can be harnessed for thermodynamic tasks. We illustrate this ability by formulating an Otto engine cycle for a quantum many-body system. The system is ramped between a strongly localized MBL regime and a thermal (or weakly localized) regime. The difference between the energy-level correlations of MBL systems and of thermal systems enables mesoscale engines to run in parallel in the thermodynamic limit, enhances the engine's reliability, and suppresses worst-case trials. We estimate analytically and calculate numerically the engine's efficiency and per-cycle power. The efficiency mirrors the efficiency of the conventional thermodynamic Otto engine. The per-cycle power scales linearly with the system size and inverse-exponentially with a localization length. This work introduces a thermodynamic lens onto MBL, which, having been studied much recently, can now be considered for use in thermodynamic tasks.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/89ta9-3f917Topological frequency conversion in a driven dissipative quantum cavity
https://resolver.caltech.edu/CaltechAUTHORS:20190325-132537557
Authors: {'items': [{'id': 'Nathan-F', 'name': {'family': 'Nathan', 'given': 'Frederik'}}, {'id': 'Martin-I', 'name': {'family': 'Martin', 'given': 'Ivar'}, 'orcid': '0000-0002-2010-6449'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2019
DOI: 10.1103/PhysRevB.99.094311
Recent work [Martin et al., Phys. Rev. X 7, 041008 (2017)] shows that a spin coupled to two externally supplied circularly polarized electromagnetic modes can effectuate a topological, quantized transfer of photons from one mode to the other. Here, we study the effect in the case when only one of the modes is externally provided, while the other is a dynamical quantum mechanical cavity mode. Focusing on the signatures and stability under experimentally accessible conditions, we show that the effect persists down to the few-photon quantum limit and that it can be used to generate highly entangled "cat states" of cavity and spin. By tuning the strength of the external drive to a "sweet spot," the quantized pumping can arise starting from an empty (zero-photon) cavity state. We also find that inclusion of external noise and dissipation does not suppress but rather stabilizes the conversion effect, even after multiple cavity modes are taken into account.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0ez7e-5r391Robust Majorana magic gates via measurements
https://resolver.caltech.edu/CaltechAUTHORS:20190424-142039996
Authors: {'items': [{'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Freedman-M-H', 'name': {'family': 'Freedman', 'given': 'Michael H.'}}]}
Year: 2019
DOI: 10.1103/physrevb.99.144521
π/8 phase gates (magic gates or T gates) are crucial to augment topological systems based on Majorana zero modes to full quantum universality. We present a scheme based on a combination of projective measurements and nonadiabatic evolution that effectively cancels smooth control errors when implementing phase gates in Majorana-based systems. Previous schemes based on adiabatic evolution are susceptible to problems arising from small but finite dynamical phases that are generically present in topologically unprotected gates. A measurement-only approach eliminates dynamical phases. For nonprotected gates, however, forced-measurement schemes are no longer effective, which leads to low success probabilities of obtaining the right succession of measurement outcomes in a measurement-only implementation. We show how to obtain a viable measurement-based scheme which dramatically increases the success probabilities by evolving the system nonadiabatically with respect to the degenerate subspace in between measurements. We outline practical applications of our scheme in recently proposed quantum computing designs based on Majorana tetrons and hexons.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5ra36-xec93From Bloch Oscillations to Many Body Localization in Clean Interacting Systems
https://resolver.caltech.edu/CaltechAUTHORS:20180821-144923153
Authors: {'items': [{'id': 'van-Nieuwenburg-E-P-L', 'name': {'family': 'van Nieuwenburg', 'given': 'Evert'}, 'orcid': '0000-0003-0323-0031'}, {'id': 'Baum-Y', 'name': {'family': 'Baum', 'given': 'Yuval'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2019
DOI: 10.1073/pnas.1819316116
PMCID: PMC6511026
In this work we demonstrate that nonrandom mechanisms that lead to single-particle localization may also lead to many-body localization, even in the absence of disorder. In particular, we consider interacting spins and fermions in the presence of a linear potential. In the noninteracting limit, these models show the well-known Wannier–Stark localization. We analyze the fate of this localization in the presence of interactions. Remarkably, we find that beyond a critical value of the potential gradient these models exhibit nonergodic behavior as indicated by their spectral and dynamical properties. These models, therefore, constitute a class of generic nonrandom models that fail to thermalize. As such, they suggest new directions for experimentally exploring and understanding the phenomena of many-body localization. We supplement our work by showing that by using machine-learning techniques the level statistics of a system may be calculated without generating and diagonalizing the Hamiltonian, which allows a generation of large statistics.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ae414-pmm25Orbital Floquet Engineering of Exchange Interactions in Magnetic Materials
https://resolver.caltech.edu/CaltechAUTHORS:20190520-132243974
Authors: {'items': [{'id': 'Chaudhary-Swati', 'name': {'family': 'Chaudhary', 'given': 'Swati'}}, {'id': 'Hsieh-David', 'name': {'family': 'Hsieh', 'given': 'David'}, 'orcid': '0000-0002-0812-955X'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2019
DOI: 10.1103/PhysRevB.100.220403
We present a scheme to control the spin-exchange interactions by manipulating the orbital degrees of freedom using a periodic drive. We discuss two different protocols for orbital Floquet engineering. In one case, a periodic drive modifies the properties of the ligand orbitals which mediate magnetic interactions between transition-metal ions. In the other case, we consider drive-induced mixing of d orbitals on each magnetic ion. We first find that an AC Stark shift of orbitals induces a change comparable to that induced from photoinduced hopping schemes, but expands the applicable frequency ranges. Next, we find that radiatively induced coherent vibrations provide a realistic path for Floquet orbital engineering with short pulses of electric fields weaker than 0.5 V/Å producing 5%–10% changes in the magnetic coupling of Mott insulators such as the rare-earth titanates.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jk5ad-65w58Floquet second-order topological insulators from nonsymmorphic space-time symmetries
https://resolver.caltech.edu/CaltechAUTHORS:20190409-112427983
Authors: {'items': [{'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2019
DOI: 10.1103/PhysRevLett.123.016806
We propose a systematic way of constructing Floquet second-order topological insulators (SOTIs) based on time-glide symmetry, a nonsymmorphic space-time symmetry that is unique in Floquet systems. In particular, we are able to show that the static enlarged Hamiltonian in the frequency domain acquires reflection symmetry, which is inherited from the time-glide symmetry of the original system. As a consequence, one can construct a variety of time-glide symmetric Floquet SOTIs using the knowledge of static SOTIs. Moreover, the time-glide symmetry only needs to be implemented approximately in practice, enhancing the prospects of experimental realizations. We consider two examples, a 2D system in class AIII and a 3D system in class A, to illustrate our ideas, and then present a general recipe for constructing Floquet SOTIs in all symmetry classes.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/j1y13-y2424Topologically protected braiding in a single wire using Floquet Majorana modes
https://resolver.caltech.edu/CaltechAUTHORS:20190429-083156058
Authors: {'items': [{'id': 'Bauer-B', 'name': {'family': 'Bauer', 'given': 'Bela'}, 'orcid': '0000-0001-9796-2115'}, {'id': 'Pereg-Barnea-T', 'name': {'family': 'Pereg-Barnea', 'given': 'T.'}}, {'id': 'Karzig-T', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Rieder-M-T', 'name': {'family': 'Rieder', 'given': 'Maria-Theresa'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Berg-E', 'name': {'family': 'Berg', 'given': 'Erez'}}, {'id': 'Oreg-Y', 'name': {'family': 'Oreg', 'given': 'Yuval'}}]}
Year: 2019
DOI: 10.1103/PhysRevB.100.041102
Majorana zero modes are a promising platform for topologically protected quantum information processing. Their non-Abelian nature, which is key for performing quantum gates, is most prominently exhibited through braiding. While originally formulated for two-dimensional systems, it has been shown that braiding can also be realized using one-dimensional wires by forming an essentially two-dimensional network. Here, we show that in driven systems far from equilibrium, one can do away with the second spatial dimension altogether by instead using quasienergy as the second dimension. To realize this, we use a Floquet topological superconductor which can exhibit Majorana modes at two special eigenvalues of the evolution operator, 0 and π, and thus can realize four Majorana modes in a single, driven quantum wire. We describe and numerically evaluate a protocol that realizes a topologically protected exchange of two Majorana zero modes in a single wire by adiabatically modulating the Floquet drive and using the π modes as auxiliary degrees of freedom.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ycyzs-xgz74Evanescent Modes and Step-like Acoustic Black Holes
https://resolver.caltech.edu/CaltechAUTHORS:20190426-161745452
Authors: {'items': [{'id': 'Curtis-J-B', 'name': {'family': 'Curtis', 'given': 'Jonathan'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Galitski-V-M', 'name': {'family': 'Galitski', 'given': 'Victor'}}]}
Year: 2019
DOI: 10.1016/j.aop.2019.04.017
We consider a model of an acoustic black hole formed by a quasi-one dimensional Bose–Einstein condensate with a step-like horizon. This system is analyzed by solving the corresponding Bogoliubov–de Gennes equation with an appropriate matching condition at the jump. When the step is between a subsonic and supersonic flow, a sonic horizon develops and in addition to the scattering coefficients we compute the distribution of the accompanying analogue Hawking radiation. Additionally, in response to the abrupt variation in flow and non-linear Bogoliubov dispersion relation, evanescent solutions of the Bogoliubov–de Gennes equation also appear and decay out from the horizon. We bound this decay length and show that these modes produce a modulation of observables outside the event horizon by their interference with outgoing Hawking flux. We go further and find specific superpositions of ingoing eigenmodes which exhibit coherent cancellation of the Hawking flux outside the horizon but nevertheless have evanescent support outside the black hole. We conclude by speculating that when quasiparticle interactions are included, evanescent modes may yield a leakage of information across the event horizon via interactions between the real outgoing Hawking flux and the virtual evanescent modes, and that we may expect this as a generic feature of models which break Lorentz invariance at the UV (Planck) scale.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/nprf4-d0186Anderson Localization on the Bethe Lattice using Cages and the Wegner Flow
https://resolver.caltech.edu/CaltechAUTHORS:20190425-135640601
Authors: {'items': [{'id': 'Savitz-S', 'name': {'family': 'Savitz', 'given': 'Samuel'}, 'orcid': '0000-0003-2112-3758'}, {'id': 'Peng-Changnan', 'name': {'family': 'Peng', 'given': 'Changnan'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2019
DOI: 10.1103/PhysRevB.100.094201
Anderson localization on treelike graphs such as the Bethe lattice, Cayley tree, or random regular graphs has attracted attention due to its apparent mathematical tractability, hypothesized connections to many-body localization, and the possibility of nonergodic extended regimes. This behavior has been conjectured to also appear in many-body localization as a "bad metal" phase, and constitutes an intermediate possibility between the extremes of ergodic quantum chaos and integrable localization. Despite decades of research, a complete consensus understanding of this model remains elusive. Here we use cages, maximally treelike structures from extremal graph theory; and numerical continuous unitary Wegner flows of the Anderson Hamiltonian to develop an intuitive picture which, after extrapolating to the infinite Bethe lattice, appears to capture ergodic, nonergodic extended, and fully localized behavior.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jv3qq-yxr73Electronic correlations in twisted bilayer graphene near the magic angle
https://resolver.caltech.edu/CaltechAUTHORS:20190426-084652512
Authors: {'items': [{'id': 'Choi-Youngjoon', 'name': {'family': 'Choi', 'given': 'Youngjoon'}}, {'id': 'Kemmer-Jeanette', 'name': {'family': 'Kemmer', 'given': 'Jeannette'}}, {'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Thomson-Alex', 'name': {'family': 'Thomson', 'given': 'Alex'}, 'orcid': '0000-0002-9938-5048'}, {'id': 'Arora-H-S', 'name': {'family': 'Arora', 'given': 'Harpreet'}, 'orcid': '0000-0002-7674-735X'}, {'id': 'Polski-R-M', 'name': {'family': 'Polski', 'given': 'Robert'}, 'orcid': '0000-0003-0887-8099'}, {'id': 'Zhang-Yiran', 'name': {'family': 'Zhang', 'given': 'Yiran'}, 'orcid': '0000-0002-8477-0074'}, {'id': 'Ren-Hechen', 'name': {'family': 'Ren', 'given': 'Hechen'}}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-F', 'name': {'family': 'von Oppen', 'given': 'Felix'}}, {'id': 'Watanabe-Kenji', 'name': {'family': 'Watanabe', 'given': 'Kenji'}, 'orcid': '0000-0003-3701-8119'}, {'id': 'Taniguchi-Takashi', 'name': {'family': 'Taniguchi', 'given': 'Takashi'}}, {'id': 'Nadj-Perge-S', 'name': {'family': 'Nadj-Perge', 'given': 'Stevan'}, 'orcid': '0000-0002-2394-9070'}]}
Year: 2019
DOI: 10.1038/s41567-019-0606-5
Twisted bilayer graphene with a twist angle of around 1.1° features a pair of isolated flat electronic bands and forms a platform for investigating strongly correlated electrons. Here, we use scanning tunnelling microscopy to probe the local properties of highly tunable twisted bilayer graphene devices and show that the flat bands deform when aligned with the Fermi level. When the bands are half-filled, we observe the development of gaps originating from correlated insulating states. Near charge neutrality, we find a previously unidentified correlated regime featuring an enhanced splitting of the flat bands. We describe this within a microscopic model that predicts a strong tendency towards nematic ordering. Our results provide insights into symmetry-breaking correlation effects and highlight the importance of electronic interactions for all filling fractions in twisted bilayer graphene.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/a69vz-3xp68Light-induced evaporative cooling of holes in the Hubbard model
https://resolver.caltech.edu/CaltechAUTHORS:20190425-142141029
Authors: {'items': [{'id': 'Werner-Philipp', 'name': {'family': 'Werner', 'given': 'Philipp'}, 'orcid': '0000-0002-2136-6568'}, {'id': 'Eckstein-Martin', 'name': {'family': 'Eckstein', 'given': 'Martin'}, 'orcid': '0000-0003-0124-5408'}, {'id': 'Müller-Markus-P', 'name': {'family': 'Müller', 'given': 'Markus'}, 'orcid': '0000-0002-0299-952X'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2019
DOI: 10.1038/s41467-019-13557-9
PMCID: PMC6895176
An elusive goal in the field of driven quantum matter is the induction of long-range order. Here, we propose a mechanism based on light-induced evaporative cooling of holes in a correlated fermionic system. Since the entropy of a filled narrow band grows rapidly with hole doping, the isentropic transfer of holes from a doped Mott insulator to such a band results in a drop of temperature. Strongly correlated Fermi liquids and symmetry-broken states could thus be produced by dipolar excitations. Using nonequilibrium dynamical mean field theory, we show that suitably designed chirped pulses may realize this cooling effect. In particular, we demonstrate the emergence of antiferromagnetic order in a system which is initially in a weakly correlated state above the maximum Néel temperature. Our work suggests a general strategy for inducing strong correlation phenomena in periodically modulated atomic gases in optical lattices or light-driven materials.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/jhm99-py963Variational-Correlations Approach to Quantum Many-body Problems
https://resolver.caltech.edu/CaltechAUTHORS:20200303-081122185
Authors: {'items': [{'id': 'Haim-Arbel', 'name': {'family': 'Haim', 'given': 'Arbel'}}, {'id': 'Kueng-R-J', 'name': {'family': 'Kueng', 'given': 'Richard'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2020
DOI: 10.48550/arXiv.2001.06510
We investigate an approach for studying the ground state of a quantum many-body Hamiltonian that is based on treating the correlation functions as variational parameters. In this approach, the challenge set by the exponentially-large Hilbert space is circumvented by approximating the positivity of the density matrix, order-by-order, in a way that keeps track of a limited set of correlation functions. In particular, the density-matrix description is replaced by a correlation matrix whose dimension is kept linear in system size, to all orders of the approximation. Unlike the conventional variational principle which provides an upper bound on the ground-state energy, in this approach one obtains a lower bound instead. By treating several one-dimensional spin 1/2 Hamiltonians, we demonstrate the ability of this approach to produce long-range correlations, and a ground-state energy that converges to the exact result. Possible extensions, including to higher-excited states are discussed.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kx3az-ex716Quantum dynamics in strongly driven random dipolar magnets
https://resolver.caltech.edu/CaltechAUTHORS:20200420-111501884
Authors: {'items': [{'id': 'Buchhold-M', 'name': {'family': 'Buchhold', 'given': 'M.'}, 'orcid': '0000-0001-5194-9388'}, {'id': 'Tang-C-S', 'name': {'family': 'Tang', 'given': 'C. S.'}}, {'id': 'Silevitch-D-M', 'name': {'family': 'Silevitch', 'given': 'D. M.'}, 'orcid': '0000-0002-6347-3513'}, {'id': 'Rosenbaum-T-F', 'name': {'family': 'Rosenbaum', 'given': 'T. F.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}]}
Year: 2020
DOI: 10.1103/PhysRevB.101.214201
The random dipolar magnet LiHo_xY_(1−x)F₄ enters a strongly frustrated regime for small Ho³⁺ concentrations with x < 0.05. In this regime, the magnetic moments of the Ho³⁺ ions experience small quantum corrections to the common Ising approximation of LiHo_xY_(1−x)F₄, which lead to a Z₂-symmetry breaking and small, degeneracy breaking energy shifts between different eigenstates. Here we show that destructive interference between two almost degenerate excitation pathways burns spectral holes in the magnetic susceptibility of strongly driven magnetic moments in LiHo_xY_(1−x)F₄. Such spectral holes in the susceptibility, microscopically described in terms of Fano resonances, can already occur in setups of only two or three frustrated moments, for which the driven level scheme has the paradigmatic Λ shape. For larger clusters of magnetic moments, the corresponding level schemes separate into almost isolated many-body Λ schemes, in the sense that either the transition matrix elements between them are negligibly small or the energy difference of the transitions is strongly off-resonant to the drive. This enables the observation of Fano resonances, caused by many-body quantum corrections to the common Ising approximation also in the thermodynamic limit. We discuss its dependence on the driving strength and frequency as well as the crucial role that is played by lattice dissipation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zm6hs-12m98Controlling ligand-mediated exchange interactions in periodically driven magnetic materials
https://resolver.caltech.edu/CaltechAUTHORS:20200928-150652942
Authors: {'items': [{'id': 'Chaudhary-Swati', 'name': {'family': 'Chaudhary', 'given': 'Swati'}}, {'id': 'Ron-Alon', 'name': {'family': 'Ron', 'given': 'Alon'}}, {'id': 'Hsieh-David', 'name': {'family': 'Hsieh', 'given': 'David'}, 'orcid': '0000-0002-0812-955X'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2020
DOI: 10.48550/arXiv.2009.00813
A periodic drive could alter the effective exchange interactions in magnetic materials. Here, we explore how exchange pathways affect the effective interactions of periodically driven magnetic materials. Aiming to apply Floquet engineering methods to two-dimensional magnetic materials, we consider realistic models and discuss the effect of a periodic drive on ligand-mediated exchange interactions. We show that depending on bond angles and the number of ligand ions involved in the exchange process, drive-induced changes can be very different from those calculated from direct-hopping models considered earlier. We study these effects and find that the presence of ligand ions must be taken into account, especially for TMTCs where ligand ion mediated next-neighbor interactions play a crucial role in determining the magnetic ground state of the system.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zkfxy-f6k81Optically induced flat bands in twisted bilayer graphene
https://resolver.caltech.edu/CaltechAUTHORS:20201016-153328923
Authors: {'items': [{'id': 'Katz-Or', 'name': {'family': 'Katz', 'given': 'Or'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Lindner-N-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}]}
Year: 2020
DOI: 10.1103/PhysRevB.102.155123
Twisted bilayer graphene at the magic twist angle features flat energy bands, which lead to superconductivity and strong correlation physics. These unique properties are typically limited to a narrow range of twist angles around the magic angle with a small allowed tolerance. Here, we report on a mechanism that enables flattening of the band structure using coherent optical illumination, leading to emergence of flat isolated Floquet-Bloch bands. We show that the effect can be realized with relatively weak optical beams at the visible-infrared range (below the material bandwidth) and persist for a wide range of small twist angles, increasing the allowed twist tolerance by an order of magnitude. We discuss the conditions under which these bands exhibit a nonzero Chern number. These optically induced flat bands could potentially host strongly correlated nonequilibrium electronic states of matter.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/8tp61-4g338Ultrafast Enhancement of Ferromagnetic Spin Exchange Induced by Ligand-to-Metal Charge Transfer
https://resolver.caltech.edu/CaltechAUTHORS:20191217-085020547
Authors: {'items': [{'id': 'Ron-Alon', 'name': {'family': 'Ron', 'given': 'A.'}, 'orcid': '0000-0002-1840-7824'}, {'id': 'Chaudhary-Swati', 'name': {'family': 'Chaudhary', 'given': 'S.'}}, {'id': 'Zhang-Gufeng', 'name': {'family': 'Zhang', 'given': 'G.'}}, {'id': 'Ning-Honglie', 'name': {'family': 'Ning', 'given': 'H.'}}, {'id': 'Zoghlin-E', 'name': {'family': 'Zoghlin', 'given': 'E.'}, 'orcid': '0000-0002-8160-584X'}, {'id': 'Wilson-S-D', 'name': {'family': 'Wilson', 'given': 'S. D.'}}, {'id': 'Averitt-R-D', 'name': {'family': 'Averitt', 'given': 'R. D.'}, 'orcid': '0000-0003-0451-1935'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Hsieh-David', 'name': {'family': 'Hsieh', 'given': 'D.'}, 'orcid': '0000-0002-0812-955X'}]}
Year: 2020
DOI: 10.1103/PhysRevLett.125.197203
We theoretically predict and experimentally demonstrate a nonthermal pathway to optically enhance superexchange interaction energies in a material based on exciting ligand-to-metal charge-transfer transitions, which introduces lower-order virtual hopping contributions that are absent in the ground state. We demonstrate this effect in the layered ferromagnetic insulator CrSiTe₃ by exciting Te-to-Cr charge-transfer transitions using ultrashort laser pulses and detecting coherent phonon oscillations that are impulsively generated by superexchange enhancement via magneto-elastic coupling. This mechanism kicks in below the temperature scale where short-range in-plane spin correlations begin to develop and disappears when the excitation energy is tuned away from the charge-transfer resonance, consistent with our predictions.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zqxn5-ecv65Quantum frequency locking and downconversion in a driven qubit-cavity system
https://resolver.caltech.edu/CaltechAUTHORS:20200519-080742316
Authors: {'items': [{'id': 'Nathan-Frederik', 'name': {'family': 'Nathan', 'given': 'Frederik'}, 'orcid': '0000-0001-9700-0231'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Rudner-Mark-S', 'name': {'family': 'Rudner', 'given': 'Mark S.'}, 'orcid': '0000-0002-5150-6234'}, {'id': 'Martin-Ivar', 'name': {'family': 'Martin', 'given': 'Ivar'}, 'orcid': '0000-0002-2010-6449'}]}
Year: 2020
DOI: 10.1103/PhysRevResearch.2.043411
We study a periodically driven qubit coupled to a quantized cavity mode. Despite its apparent simplicity, this system supports a rich variety of exotic phenomena, such as topological frequency conversion as recently discovered in Martin et al. [Phys. Rev. X 7, 041008 (2017)]. Here we report on a qualitatively different phenomenon that occurs in this platform, where the cavity mode's oscillations lock their frequency to a rational fraction r/q of the driving frequency Ω. This phenomenon, which we term quantum frequency locking, is characterized by the emergence of q-tuplets of stationary (Floquet) states whose quasienergies are separated by Ω/q, up to exponentially small corrections. The Wigner functions of these states are nearly identical, and exhibit highly regular and symmetric structure in phase space. Similarly to Floquet time crystals, these states underlie discrete time-translation symmetry breaking in the model. We develop a semiclassical approach for analyzing and predicting quantum frequency locking in the model, and use it to identify the conditions under which it occurs.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/n3vhy-dt084Phonon-induced Floquet topological phases protected by space-time symmetries
https://resolver.caltech.edu/CaltechAUTHORS:20191217-115034328
Authors: {'items': [{'id': 'Chaudhary-Swati', 'name': {'family': 'Chaudhary', 'given': 'Swati'}}, {'id': 'Haim-Arbel', 'name': {'family': 'Haim', 'given': 'Arbel'}}, {'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2020
DOI: 10.1103/PhysRevResearch.2.043431
For systems with spatial and nonspatial symmetries, the topological classification depends not only on these symmetries but also on the commutation/anticommutation relations between spatial and nonspatial symmetries. The coexistence of spatial and nonspatial symmetries together with appropriate commutation/anticommutation relations between them can give rise to crystalline and higher-order topological phases, which host gapless boundary modes. Alternatively, space-time symmetries in a Floquet system can take the role of spatial symmetries in deciding the topological classification. Promoting a spatial symmetry to a space-time symmetry can alter the commutation relations, which in turn can modify the topological properties of the system. We show how a coherently excited phonon mode can be used to promote a spatial symmetry with which the static system is always trivial to a space-time symmetry which supports a nontrivial Floquet topological phase. We demonstrate this effect by considering two systems: The first is a second-order topological superconductor, and the second is a first-order crystalline topological insulator. In both these cases, a coherently excited phonon mode is responsible for promoting the reflection symmetry to a time-glide symmetry. This newly introduced symmetry allows the previously trivial system to host gapless modes. In the first case, these are protected corner modes, while in the second case, these are gapless edge modes.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/65542-z5p22Signatures of Ultrafast Reversal of Excitonic Order in Ta₂NiSe₅
https://resolver.caltech.edu/CaltechAUTHORS:20201224-090002408
Authors: {'items': [{'id': 'Ning-Honglie', 'name': {'family': 'Ning', 'given': 'H.'}}, {'id': 'Mehio-Omar', 'name': {'family': 'Mehio', 'given': 'O.'}}, {'id': 'Buchhold-Michael', 'name': {'family': 'Buchhold', 'given': 'M.'}, 'orcid': '0000-0001-5194-9388'}, {'id': 'Kurumaji-Takashi', 'name': {'family': 'Kurumaji', 'given': 'T.'}, 'orcid': '0000-0002-2157-3727'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'G.'}}, {'id': 'Checkelsky-Joseph-G', 'name': {'family': 'Checkelsky', 'given': 'J.\u2009G.'}, 'orcid': '0000-0003-0325-5204'}, {'id': 'Hsieh-David', 'name': {'family': 'Hsieh', 'given': 'D.'}, 'orcid': '0000-0002-0812-955X'}]}
Year: 2020
DOI: 10.1103/physrevlett.125.267602
In the presence of electron-phonon coupling, an excitonic insulator harbors two degenerate ground states described by an Ising-type order parameter. Starting from a microscopic Hamiltonian, we derive the equations of motion for the Ising order parameter in the phonon coupled excitonic insulator Ta₂NiSe₅ and show that it can be controllably reversed on ultrashort timescales using appropriate laser pulse sequences. Using a combination of theory and time-resolved optical reflectivity measurements, we report evidence of such order parameter reversal in Ta₂NiSe₅ based on the anomalous behavior of its coherently excited order-parameter-coupled phonons. Our Letter expands the field of ultrafast order parameter control beyond spin and charge ordered materials.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/5tzpp-vvv59Extracting many-body localization lengths with an imaginary vector potential
https://resolver.caltech.edu/CaltechAUTHORS:20200518-153736634
Authors: {'items': [{'id': 'Heußen-Sascha', 'name': {'family': 'Heußen', 'given': 'Sascha'}, 'orcid': '0000-0002-7581-2148'}, {'id': 'White-Christopher-David', 'name': {'family': 'White', 'given': 'Christopher David'}, 'orcid': '0000-0002-8372-2492'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2021
DOI: 10.1103/PhysRevB.103.064201
One challenge of studying the many-body localization transition is defining the length scale that diverges upon the transition to the ergodic phase. In this manuscript we explore the localization properties of a ring with onsite disorder subject to an imaginary magnetic flux. We connect the imaginary flux which delocalizes single-particle orbitals of an Anderson-localized ring with the localization length of an open chain. We thus identify the delocalizing imaginary flux per site with an inverse localization length characterizing the transport properties of the open chain. We put this intuition to use by exploring the phase diagram of a disordered interacting chain, and we find that the inverse imaginary flux per bond provides an accessible description of the transition and its diverging localization length.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/rsqyx-b6k74Anomalous exciton transport in response to a uniform in-plane electric field
https://resolver.caltech.edu/CaltechAUTHORS:20201111-135554466
Authors: {'items': [{'id': 'Chaudhary-Swati', 'name': {'family': 'Chaudhary', 'given': 'Swati'}}, {'id': 'Knapp-Christina', 'name': {'family': 'Knapp', 'given': 'Christina'}, 'orcid': '0000-0002-5982-8107'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2021
DOI: 10.1103/PhysRevB.103.165119
Excitons are neutral objects that, naively, should have no response to a uniform electric field. Could the Berry curvature of the underlying electronic bands alter this conclusion? In this work, we show that Berry curvature can indeed lead to anomalous transport for excitons in two-dimensional materials subject to a uniform in-plane electric field. By considering the constituent electron and hole dynamics, we demonstrate that there exists a regime for which the corresponding anomalous velocities are in the same direction. We establish the resulting center-of-mass motion of the exciton through both a semiclassical and fully quantum mechanical analysis, and elucidate the critical role of Bloch oscillations in achieving this effect. We identify transition metal dichalcogenide heterobilayers as candidate materials to observe the effect.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/91pcf-7nx16Floquet Majorana bound states in voltage-biased planar Josephson junctions
https://resolver.caltech.edu/CaltechAUTHORS:20210105-133420695
Authors: {'items': [{'id': 'Peng-Changnan', 'name': {'family': 'Peng', 'given': 'Changnan'}, 'orcid': '0000-0002-9331-2614'}, {'id': 'Haim-Arbel', 'name': {'family': 'Haim', 'given': 'Arbel'}}, {'id': 'Karzig-Torsten', 'name': {'family': 'Karzig', 'given': 'Torsten'}, 'orcid': '0000-0003-0834-0547'}, {'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2021
DOI: 10.1103/PhysRevResearch.3.023108
We study a planar Josephson junction under an applied DC voltage bias in the presence of an in-plane magnetic field. Upon tuning the bias voltage across the junction V_J, the two ends of the junction are shown to simultaneously host both zero and π Majorana modes. These modes can be probed using either a scanning-tunneling-microscopy measurement or through resonant Andreev tunneling from a lead coupled to the junction. While these modes are mostly bound to the junction's ends, they can hybridize with the bulk by absorbing or emitting photons. We analyze this process both numerically and analytically, demonstrating that it can become negligible under typical experimental conditions. Transport signatures of the zero and π Majorana states are shown to be robust to moderate disorder.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ms24v-5cc11Bulk-Boundary Correspondence for Non-Hermitian Hamiltonians via Green Functions
https://resolver.caltech.edu/CaltechAUTHORS:20190426-083909000
Authors: {'items': [{'id': 'Zirnstein-Heinrich-Gregor', 'name': {'family': 'Zirnstein', 'given': 'Heinrich-Gregor'}, 'orcid': '0000-0001-7055-9959'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Rosenow-Bernd', 'name': {'family': 'Rosenow', 'given': 'Bernd'}}]}
Year: 2021
DOI: 10.1103/PhysRevLett.126.216407
Genuinely non-Hermitian topological phases can be realized in open systems with sufficiently strong gain and loss; in such phases, the Hamiltonian cannot be deformed into a gapped Hermitian Hamiltonian without energy bands touching each other. Comparing Green functions for periodic and open boundary conditions we find that, in general, there is no correspondence between topological invariants computed for periodic boundary conditions, and boundary eigenstates observed for open boundary conditions. Instead, we find that the non-Hermitian winding number in one dimension signals a topological phase transition in the bulk: It implies spatial growth of the bulk Green function.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fgs93-e3677Stirring by Staring: Measurement Induced Chirality
https://resolver.caltech.edu/CaltechAUTHORS:20220113-182208459
Authors: {'items': [{'id': 'Wampler-Matthew', 'name': {'family': 'Wampler', 'given': 'Matthew'}}, {'id': 'Khor-Brian-J-J', 'name': {'family': 'Khor', 'given': 'Brian J. J.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Klich-Israel', 'name': {'family': 'Klich', 'given': 'Israel'}, 'orcid': '0000-0002-8979-0170'}]}
Year: 2021
DOI: 10.48550/arXiv.2108.05906
Controlling the dynamics of quantum systems is a current frontier of quantum many-body physics. Recent advancements in experimental techniques suggest exciting new directions in drive-induced quantum states. Here, we present a simple scheme that relies solely on occupation measurements to induce a chiral quantum phase. Namely, we show that by utilizing a pattern of repeated quantum measurements we can produce chiral edge transport of fermions hopping on a Lieb lattice. We study in detail the dependence on measurement frequency, showing that in the Zeno limit the system can be described by a classical stochastic dynamics, yielding protected transport. As the frequency of measurements is reduced, the charge flow is reduced and vanishes when no measurements are done.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0vv01-b1807Photon pumping in a weakly-driven quantum cavity–spin system
https://resolver.caltech.edu/CaltechAUTHORS:20210511-095252246
Authors: {'items': [{'id': 'Psaroudaki-Christina', 'name': {'family': 'Psaroudaki', 'given': 'Christina'}, 'orcid': '0000-0002-7073-6422'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2021
DOI: 10.1016/j.aop.2021.168553
We investigate the photon pumping effect in a topological model consisting of a periodically driven spin-1/2 coupled to a quantum cavity mode out of the adiabatic limit. In the strong-drive adiabatic limit, a quantized frequency conversion of photons is expected as the temporal analog of the Hall current. We numerically establish a novel photon pumping phenomenon in the experimentally accessible nonadiabatic driving regime for a broad region of the parameter space. The photon frequency conversion efficiency exhibits strong fluctuations and high efficiency that can reach up 80% of the quantized value for commensurate frequency combinations. We link the pumping properties to the delocalization of the corresponding Floquet states which display multifractal behavior as the result of hybridization between localized and delocalized sectors. Finally we demonstrate that the quantum coherence properties of the initial state are preserved during the frequency conversion process in both the strong and ultra-weak-drive limit.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/1bm08-52f02Universal nonadiabatic energy pumping in a quasiperiodically driven extended system
https://resolver.caltech.edu/CaltechAUTHORS:20211202-233649522
Authors: {'items': [{'id': 'Qi-Zihao', 'name': {'family': 'Qi', 'given': 'Zihao'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}]}
Year: 2021
DOI: 10.1103/physrevb.104.224301
The paradigm of Floquet engineering of topological states of matter can be generalized into the time-quasiperiodic scenario, where a lower-dimensional time-dependent system maps onto a higher-dimensional one by combining the physical dimensions with additional synthetic dimensions generated by multiple incommensurate driving frequencies. Differently from most previous works in which gapped topological phases were considered, we propose an experimentally realizable, one-dimensional chain driven by two frequencies, which maps onto a gapless Weyl semimetal in a synthetic dimension. Based on analytical reasoning and numerical simulations, we find that the nonadiabatic quantum dynamics of this system exhibit energy pumping behaviors characterized by universal functions. We also numerically find that such behaviors are robust against a considerable amount of spatial disorder.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/bpwcs-7v806Ascendance of Superconductivity in Magic-Angle Graphene Multilayers
https://resolver.caltech.edu/CaltechAUTHORS:20220113-234609742
Authors: {'items': [{'id': 'Zhang-Yiran', 'name': {'family': 'Zhang', 'given': 'Yiran'}, 'orcid': '0000-0002-8477-0074'}, {'id': 'Polski-Robert-M', 'name': {'family': 'Polski', 'given': 'Robert'}, 'orcid': '0000-0003-0887-8099'}, {'id': 'Lewandowski-Cyprian', 'name': {'family': 'Lewandowski', 'given': 'Cyprian'}, 'orcid': '0000-0002-6944-9805'}, {'id': 'Thomson-Alex', 'name': {'family': 'Thomson', 'given': 'Alex'}, 'orcid': '0000-0002-9938-5048'}, {'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Choi-Youngjoon', 'name': {'family': 'Choi', 'given': 'Youngjoon'}}, {'id': 'Kim-Hyunjin', 'name': {'family': 'Kim', 'given': 'Hyunjin'}, 'orcid': '0000-0001-9886-0487'}, {'id': 'Watanabe-Kenji', 'name': {'family': 'Watanabe', 'given': 'Kenji'}, 'orcid': '0000-0003-3701-8119'}, {'id': 'Taniguchi-Takashi', 'name': {'family': 'Taniguchi', 'given': 'Takashi'}, 'orcid': '0000-0002-1467-3105'}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'von-Oppen-Felix', 'name': {'family': 'von Oppen', 'given': 'Felix'}, 'orcid': '0000-0002-2537-7256'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Nadj-Perge-S', 'name': {'family': 'Nadj-Perge', 'given': 'Stevan'}, 'orcid': '0000-0002-2394-9070'}]}
Year: 2022
DOI: 10.48550/arXiv.2112.09270
Graphene moire superlattices have emerged as a platform hosting and abundance of correlated insulating, topological, and superconducting phases. While the origins of strong correlations and non-trivial topology are shown to be directly linked to flat moire bands, the nature and mechanism of superconductivity remain enigmatic. In particular, only alternating twisted stacking geometries of bilayer and trilayer graphene are found to exhibit robust superconductivity manifesting as zero resistance and Fraunhofer interference patterns. Here we demonstrate that magic-angle twisted tri-, quadri-, and pentalayers placed on monolayer tungsten diselenide exhibit flavour polarization and superconductivity. We also observe insulating states in the trilayer and quadrilayer arising at finite electric displacement fields, despite the presence of dispersive bands introduced by additional graphene layers. Moreover, the three multilayer geometries allow us to identify universal features in the family of graphene moire structures arising from the intricate relations between superconducting states, symmetry-breaking transitions, and van Hove singularities. Remarkably, as the number of layers increases, superconductivity emerges over a dramatically enhanced filling-factor range. In particular, in twisted pentalayers, superconductivity extends well beyond the filling of four electrons per moire unit cell, demonstrating the non-trivial role of the additional bands. Our results highlight the importance of the interplay between flat and dispersive bands in extending superconducting regions in graphene moire superlattices and open new frontiers for developing graphene-based superconductors.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/n990w-e2f28Building a fault-tolerant quantum computer using concatenated cat codes
https://resolver.caltech.edu/CaltechAUTHORS:20201209-172305164
Authors: {'items': [{'id': 'Chamberland-Christopher', 'name': {'family': 'Chamberland', 'given': 'Christopher'}, 'orcid': '0000-0003-3239-5783'}, {'id': 'Noh-Kyungjoo', 'name': {'family': 'Noh', 'given': 'Kyungjoo'}, 'orcid': '0000-0002-6318-8472'}, {'id': 'Arrangoiz-Arriola-Patricio', 'name': {'family': 'Arrangoiz-Arriola', 'given': 'Patricio'}}, {'id': 'Campbell-Earl-T', 'name': {'family': 'Campbell', 'given': 'Earl T.'}}, {'id': 'Hann-Connor-T', 'name': {'family': 'Hann', 'given': 'Connor T.'}, 'orcid': '0000-0003-0665-7161'}, {'id': 'Iverson-Joseph-K', 'name': {'family': 'Iverson', 'given': 'Joseph K.'}, 'orcid': '0000-0003-4665-8839'}, {'id': 'Putterman-Harald', 'name': {'family': 'Putterman', 'given': 'Harald'}, 'orcid': '0000-0002-5841-181X'}, {'id': 'Bohdanowicz-Thomas-C', 'name': {'family': 'Bohdanowicz', 'given': 'Thomas C.'}}, {'id': 'Flammia-Steven-T', 'name': {'family': 'Flammia', 'given': 'Steven T.'}, 'orcid': '0000-0002-3975-0226'}, {'id': 'Keller-Andrew-J', 'name': {'family': 'Keller', 'given': 'Andrew J.'}, 'orcid': '0000-0003-3030-1149'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Preskill-J', 'name': {'family': 'Preskill', 'given': 'John'}, 'orcid': '0000-0002-2421-4762'}, {'id': 'Jiang-Liang', 'name': {'family': 'Jiang', 'given': 'Liang'}, 'orcid': '0000-0002-0000-9342'}, {'id': 'Safavi-Naeini-Amir-H', 'name': {'family': 'Safavi-Naeini', 'given': 'Amir H.'}, 'orcid': '0000-0001-6176-1274'}, {'id': 'Painter-O', 'name': {'family': 'Painter', 'given': 'Oskar'}, 'orcid': '0000-0002-1581-9209'}, {'id': 'Brandão-F-G-S-L', 'name': {'family': 'Brandão', 'given': 'Fernando G. S. L.'}, 'orcid': '0000-0003-3866-9378'}]}
Year: 2022
DOI: 10.1103/PRXQuantum.3.010329
We present a comprehensive architectural analysis for a proposed fault-tolerant quantum computer based on cat codes concatenated with outer quantum error-correcting codes. For the physical hardware, we propose a system of acoustic resonators coupled to superconducting circuits with a two-dimensional layout. Using estimated physical parameters for the hardware, we perform a detailed error analysis of measurements and gates, including cnot and Toffoli gates. Having built a realistic noise model, we numerically simulate quantum error correction when the outer code is either a repetition code or a thin rectangular surface code. Our next step toward universal fault-tolerant quantum computation is a protocol for fault-tolerant Toffoli magic state preparation that significantly improves upon the fidelity of physical Toffoli gates at very low qubit cost. To achieve even lower overheads, we devise a new magic state distillation protocol for Toffoli states. Combining these results together, we obtain realistic full-resource estimates of the physical error rates and overheads needed to run useful fault-tolerant quantum algorithms. We find that with around 1000 superconducting circuit components, one could construct a fault-tolerant quantum computer that can run circuits, which are currently intractable for classical computers. Hardware with 18 000 superconducting circuit components, in turn, could simulate the Hubbard model in a regime beyond the reach of classical computing.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/m0b5h-7gr74Decoupling of static and dynamic criticality in a driven Mott insulator
https://resolver.caltech.edu/CaltechAUTHORS:20220113-234606083
Authors: {'items': [{'id': 'de-la-Torre-Alberto', 'name': {'family': 'de la Torre', 'given': 'Alberto'}, 'orcid': '0000-0002-6751-8205'}, {'id': 'Seyler-Kyle-L', 'name': {'family': 'Seyler', 'given': 'Kyle L.'}, 'orcid': '0000-0003-1553-4518'}, {'id': 'Buchhold-Michael', 'name': {'family': 'Buchhold', 'given': 'Michael'}, 'orcid': '0000-0001-5194-9388'}, {'id': 'Baum-Yuval', 'name': {'family': 'Baum', 'given': 'Yuval'}, 'orcid': '0000-0003-4631-8551'}, {'id': 'Zhang-Gu-Feng', 'name': {'family': 'Zhang', 'given': 'Gufeng'}, 'orcid': '0000-0001-8188-2559'}, {'id': 'Lauriita-Nicholas-J', 'name': {'family': 'Laurita', 'given': 'Nicholas J.'}, 'orcid': '0000-0002-7794-7951'}, {'id': 'Harter-John-W', 'name': {'family': 'Harter', 'given': 'John W.'}, 'orcid': '0000-0002-7146-9370'}, {'id': 'Zhao-Liuyan', 'name': {'family': 'Zhao', 'given': 'Liuyan'}, 'orcid': '0000-0001-9512-3537'}, {'id': 'Phinney-Isabelle', 'name': {'family': 'Phinney', 'given': 'Isabelle'}}, {'id': 'Chen-Xiang', 'name': {'family': 'Chen', 'given': 'Xiang'}, 'orcid': '0000-0003-3997-8148'}, {'id': 'Wilson-Stephen-D', 'name': {'family': 'Wilson', 'given': 'Stephen D.'}, 'orcid': '0000-0003-3733-930X'}, {'id': 'Cao-Gang', 'name': {'family': 'Cao', 'given': 'Gang'}, 'orcid': '0000-0001-9779-430X'}, {'id': 'Averitt-Richard-D', 'name': {'family': 'Averitt', 'given': 'Richard D.'}, 'orcid': '0000-0003-0451-1935'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Hsieh-David', 'name': {'family': 'Hsieh', 'given': 'David'}, 'orcid': '0000-0002-0812-955X'}]}
Year: 2022
DOI: 10.1038/s42005-022-00813-6
Strongly driven antiferromagnetic Mott insulators have the potential to exhibit exotic transient phenomena that are forbidden in thermal equilibrium. However, such far-from-equilibrium regimes, where conventional time-dependent Ginzburg-Landau descriptions fail, are experimentally challenging to prepare and to probe especially in solid state systems. Here we use a combination of time-resolved second harmonic optical polarimetry and coherent magnon spectroscopy to interrogate n-type photo-doping induced ultrafast magnetic order parameter dynamics in the antiferromagnetic Mott insulator Sr₂IrO₄. We find signatures of an unusual far-from-equilibrium critical regime in which the divergences of the magnetic correlation length and relaxation time are decoupled. This violation of conventional thermal critical behavior arises from the interplay of photo-doping and non-thermal magnon population induced demagnetization effects. Our findings, embodied in a non-equilibrium phase diagram, provide a blueprint for engineering the out-of-equilibrium properties of quantum matter, with potential applications to terahertz spintronics technologies.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/fdnnj-y1e72Topological frequency conversion in Weyl semimetals
https://resolver.caltech.edu/CaltechAUTHORS:20220224-200907852
Authors: {'items': [{'id': 'Nathan-Frederik', 'name': {'family': 'Nathan', 'given': 'Frederik'}, 'orcid': '0000-0001-9700-0231'}, {'id': 'Martin-Ivar', 'name': {'family': 'Martin', 'given': 'Ivar'}, 'orcid': '0000-0002-2010-6449'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2022
DOI: 10.48550/arXiv.2201.07804
We show that a Weyl semimetal irradiated at two distinct frequencies can convert energy between the frequencies at a potentially large rate. The phenomenon is a realization of topological frequency conversion from [Martin et al, PRX 7 041008 (2017)]. When the effect is realized, each electron near a Weyl point acts as a topological frequency converter, and converts energy at a universal rate given by Planck's constant multiplied by the product of the two frequencies. Our results indicate that Weyl points in TaAs support topological frequency conversion in the THz regime at achievable intensities of order 100 W/mm2. When the topological energy conversion rate exceeds the dissipation rate, the effect can be used for optical amplification. This amplification regime can be achieved when the relaxation rate of the system is larger than the characteristic driving period. This phenomenon further amplifies Weyl semimetals' promise for optical amplification and terahertz (THz) generation.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/0pn1a-12057Universal transport in periodically driven systems without long-lived quasiparticles
https://resolver.caltech.edu/CaltechAUTHORS:20220329-173619034
Authors: {'items': [{'id': 'Esin-Iliya', 'name': {'family': 'Esin', 'given': 'Iliya'}, 'orcid': '0000-0003-2959-0617'}, {'id': 'Kuhlenkamp-Clemens', 'name': {'family': 'Kuhlenkamp', 'given': 'Clemens'}, 'orcid': '0000-0001-5529-4358'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Berg-Erez', 'name': {'family': 'Berg', 'given': 'Erez'}, 'orcid': '0000-0001-8956-3384'}, {'id': 'Rudner-Mark-S', 'name': {'family': 'Rudner', 'given': 'Mark S.'}, 'orcid': '0000-0002-5150-6234'}, {'id': 'Lindner-Netanel-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}]}
Year: 2022
DOI: 10.48550/arXiv.2203.01313
An intriguing regime of universal charge transport at high entropy density has been proposed for periodically driven interacting one-dimensional systems with Bloch bands separated by a large single-particle band gap. For weak interactions, a simple picture based on well-defined Floquet quasiparticles suggests that the system should host a quasisteady state current that depends only on the populations of the system's Floquet-Bloch bands and their associated quasienergy winding numbers. Here we show that such topological transport persists into the strongly interacting regime where the single-particle lifetime becomes shorter than the drive period. Analytically, we show that the value of the current is insensitive to interaction-induced band renormalizations and lifetime broadening when certain conditions are met by the system's non-equilibrium distribution function. We show that these conditions correspond to a quasisteady state. We support these predictions through numerical simulation of a system of strongly interacting fermions in a periodically-modulated chain of Sachdev-Ye-Kitaev dots. Our work establishes universal transport at high entropy density as a robust far from equilibrium topological phenomenon, which can be readily realized with cold atoms in optical lattices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/3y6s2-zzm18Shift-current response as a probe of quantum geometry and electron-electron interactions in twisted bilayer graphene
https://resolver.caltech.edu/CaltechAUTHORS:20210825-184647720
Authors: {'items': [{'id': 'Chaudhary-Swati', 'name': {'family': 'Chaudhary', 'given': 'Swati'}}, {'id': 'Lewandowski-Cyprian', 'name': {'family': 'Lewandowski', 'given': 'Cyprian'}, 'orcid': '0000-0002-6944-9805'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2022
DOI: 10.1103/PhysRevResearch.4.013164
Moiré materials, and in particular twisted bilayer graphene (TBG), exhibit a range of fascinating phenomena that emerge from the interplay of band topology and interactions. We show that the nonlinear second-order photoresponse is an appealing probe of this rich interplay. A dominant part of the photoresponse is the shift current, which is determined by the geometry of the electronic wave functions and carrier properties and thus becomes strongly modified by electron-electron interactions. We analyze its dependence on the twist angle and doping and investigate the role of interactions. In the absence of interactions, the response of the system is dictated by two energy scales: (i) the mean energy of direct transitions between the hole and electron flat bands and (ii) the gap between flat and dispersive bands. Including electron-electron interactions both enhances the response at the noninteracting characteristic frequencies and produces new resonances. We attribute these changes to the filling-dependent band renormalization in TBG. Our results highlight the connection between nontrivial geometric properties of TBG and its optical response, as well as demonstrate how optical probes can access the role of interactions in moiré materials.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/00m6e-msq07Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene
https://resolver.caltech.edu/CaltechAUTHORS:20220524-180258498
Authors: {'items': [{'id': 'Polski-Robert-M', 'name': {'family': 'Polski', 'given': 'Robert'}, 'orcid': '0000-0003-0887-8099'}, {'id': 'Zhang-Yiran', 'name': {'family': 'Zhang', 'given': 'Yiran'}, 'orcid': '0000-0002-8477-0074'}, {'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Arora-Harpreet-Singh', 'name': {'family': 'Arora', 'given': 'Harpreet Singh'}, 'orcid': '0000-0002-7674-735X'}, {'id': 'Choi-Youngjoon', 'name': {'family': 'Choi', 'given': 'Youngjoon'}, 'orcid': '0000-0001-9783-5992'}, {'id': 'Kim-Hyunjin', 'name': {'family': 'Kim', 'given': 'Hyunjin'}, 'orcid': '0000-0001-9886-0487'}, {'id': 'Watanabe-Kenji', 'name': {'family': 'Watanabe', 'given': 'Kenji'}, 'orcid': '0000-0003-3701-8119'}, {'id': 'Taniguchi-Takashi', 'name': {'family': 'Taniguchi', 'given': 'Takashi'}, 'orcid': '0000-0002-1467-3105'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'von-Oppen-Felix', 'name': {'family': 'von Oppen', 'given': 'Felix'}, 'orcid': '0000-0002-2537-7256'}, {'id': 'Nadj-Perge-S', 'name': {'family': 'Nadj-Perge', 'given': 'Stevan'}, 'orcid': '0000-0002-2394-9070'}]}
Year: 2022
DOI: 10.48550/arXiv.2205.05225
Twisted bilayer graphene (TBG) near the magic twist angle of ∼1.1° exhibits a rich phase diagram. However, the interplay between different phases and their dependence on twist angle is still elusive. Here, we explore the stability of various TBG phases and demonstrate that superconductivity near filling of two electrons per moiré unit cell alongside Fermi surface reconstructions, as well as entropy-driven high-temperature phase transitions and linear-in-T resistance occur over a range of twist angles which extends far beyond those exhibiting correlated insulating phases. In the vicinity of the magic angle, we also find a metallic phase that displays a hysteretic anomalous Hall effect and incipient Chern insulating behaviour. Such a metallic phase can be rationalized in terms of the interplay between interaction-driven deformations of TBG bands leading to Berry curvature redistribution and Fermi surface reconstruction. Our results provide an extensive perspective on the hierarchy of correlated phases in TBG as classified by their robustness against deviations from the magic angle or, equivalently, their electronic interaction requirements.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/06ybb-rx004Stirring by Staring: Measurement-Induced Chirality
https://resolver.caltech.edu/CaltechAUTHORS:20220920-630646700
Authors: {'items': [{'id': 'Wampler-Matthew', 'name': {'family': 'Wampler', 'given': 'Matthew'}, 'orcid': '0000-0001-6303-3561'}, {'id': 'Khor-Brian-J-J', 'name': {'family': 'Khor', 'given': 'Brian J.\u2009J.'}}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Klich-Israel', 'name': {'family': 'Klich', 'given': 'Israel'}, 'orcid': '0000-0002-8979-0170'}]}
Year: 2022
DOI: 10.1103/physrevx.12.031031
In quantum mechanics, the observer necessarily plays an active role in the dynamics of the system, making it difficult to probe a system without disturbing it. Here, we leverage this apparent difficulty as a tool for driving an initially trivial system into a chiral phase. In particular, we show that by utilizing a pattern of repeated occupation measurements we can produce chiral edge transport of fermions hopping on a Lieb lattice. The procedure is similar in spirit to the use of periodic driving to induce chiral edge transport in Floquet topological insulators, while also exhibiting novel phenomena due to the nonunitary nature of the quantum measurements. We study in detail the dependence of the procedure on measurement frequency, showing that in the Zeno limit the system can be described by a classical stochastic dynamics, yielding protected transport. As the frequency of measurements is reduced, the charge flow is reduced and vanishes when no measurements are done.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/g1vbr-pvb60Generating coherent phonon waves in narrow-band materials: a twisted bilayer graphene phaser
https://resolver.caltech.edu/CaltechAUTHORS:20220816-183030641
Authors: {'items': [{'id': 'Esin-Iliya', 'name': {'family': 'Esin', 'given': 'Iliya'}, 'orcid': '0000-0003-2959-0617'}, {'id': 'Esterlis-Ilya', 'name': {'family': 'Esterlis', 'given': 'Ilya'}, 'orcid': '0000-0003-4775-9105'}, {'id': 'Demler-Eugene-A', 'name': {'family': 'Demler', 'given': 'Eugene'}, 'orcid': '0000-0002-2499-632X'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2022
DOI: 10.48550/arXiv.2207.11245
Twisted bilayer graphene (TBG) exhibits extremely low Fermi velocities for electrons, with the speed of sound surpassing the Fermi velocity. This regime enables the use of TBG for amplifying vibrational waves of the lattice through stimulated emission, following the same principles of operation of free-electron lasers. Our work proposes a lasing mechanism relying on the slow-electron bands to produce a coherent beam of acoustic phonons. We propose a device based on undulated electrons in TBG, which we dub the phaser. The device generates phonon beams in a terahertz (THz) frequency range, which can then be used to produce THz electromagnetic radiation. The ability to generate coherent phonons in solids breaks new ground in controlling quantum memories, probing quantum states, realizing non-equilibrium phases of matter, and designing new types of THz optical devices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/zkt65-24m51Promotion of superconductivity in magic-angle graphene multilayers
https://resolver.caltech.edu/CaltechAUTHORS:20221215-427737300.1
Authors: {'items': [{'id': 'Zhang-Yiran', 'name': {'family': 'Zhang', 'given': 'Yiran'}, 'orcid': '0000-0002-8477-0074'}, {'id': 'Polski-Robert-M', 'name': {'family': 'Polski', 'given': 'Robert'}, 'orcid': '0000-0003-0887-8099'}, {'id': 'Lewandowski-Cyprian', 'name': {'family': 'Lewandowski', 'given': 'Cyprian'}, 'orcid': '0000-0002-6944-9805'}, {'id': 'Thomson-Alex', 'name': {'family': 'Thomson', 'given': 'Alex'}, 'orcid': '0000-0002-9938-5048'}, {'id': 'Peng-Yang', 'name': {'family': 'Peng', 'given': 'Yang'}, 'orcid': '0000-0002-8868-2928'}, {'id': 'Choi-Youngjoon', 'name': {'family': 'Choi', 'given': 'Youngjoon'}, 'orcid': '0000-0001-9783-5992'}, {'id': 'Kim-Hyunjin', 'name': {'family': 'Kim', 'given': 'Hyunjin'}, 'orcid': '0000-0001-9886-0487'}, {'id': 'Watanabe-Kenji', 'name': {'family': 'Watanabe', 'given': 'Kenji'}, 'orcid': '0000-0003-3701-8119'}, {'id': 'Taniguchi-Takashi', 'name': {'family': 'Taniguchi', 'given': 'Takashi'}, 'orcid': '0000-0002-1467-3105'}, {'id': 'Alicea-J', 'name': {'family': 'Alicea', 'given': 'Jason'}, 'orcid': '0000-0001-9979-3423'}, {'id': 'von-Oppen-Felix', 'name': {'family': 'von Oppen', 'given': 'Felix'}, 'orcid': '0000-0002-2537-7256'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Nadj-Perge-S', 'name': {'family': 'Nadj-Perge', 'given': 'Stevan'}, 'orcid': '0000-0002-2394-9070'}]}
Year: 2022
DOI: 10.1126/science.abn8585
Graphene moiré superlattices show an abundance of correlated insulating, topological, and superconducting phases. Whereas the origins of strong correlations and nontrivial topology can be directly linked to flat bands, the nature of superconductivity remains enigmatic. We demonstrate that magic-angle devices made of twisted tri-, quadri-, and pentalayer graphene placed on monolayer tungsten diselenide exhibit flavor polarization and superconductivity. We also observe insulating states in the tril- and quadrilayer arising at finite electric displacement fields. As the number of layers increases, superconductivity emerges over an enhanced filling-factor range, and in the pentalayer it extends well beyond the filling of four electrons per moiré unit cell. Our results highlight the role of the interplay between flat and more dispersive bands in extending superconducting regions in graphene moiré superlattices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/202s5-wxx58Topological frequency conversion in Weyl semimetals
https://resolver.caltech.edu/CaltechAUTHORS:20221121-712406200.5
Authors: {'items': [{'id': 'Nathan-Frederik', 'name': {'family': 'Nathan', 'given': 'Frederik'}, 'orcid': '0000-0001-9700-0231'}, {'id': 'Martin-Ivar', 'name': {'family': 'Martin', 'given': 'Ivar'}, 'orcid': '0000-0002-2010-6449'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2022
DOI: 10.1103/physrevresearch.4.043060
We theoretically predict a working principle for optical amplification, based on Weyl semimetals: When a Weyl semimetal is suitably irradiated at two frequencies, electrons close to the Weyl points convert energy between the frequencies through the mechanism of topological frequency conversion from [Martin et al., Phys. Rev. X 7, 041008 (2017)]. Each electron converts energy at a quantized rate given by an integer multiple of Planck's constant multiplied by the product of the two frequencies. In simulations, we show that optimal, but feasible band structures, can support topological frequency conversion in the "THz gap" at intensities down to 2 W/mm²; the gain from the effect can exceed the dissipative loss when the frequencies are larger than the relaxation time of the system. Topological frequency conversion forms a paradigm for optical amplification, which further extends Weyl semimetals' promise for technological applications.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/e28ry-gkg44Generating Coherent Phonon Waves in Narrow-Band Materials: A Twisted Bilayer Graphene Phaser
https://resolver.caltech.edu/CaltechAUTHORS:20230518-332288000.2
Authors: {'items': [{'id': 'Esin-Iliya', 'name': {'family': 'Esin', 'given': 'Iliya'}, 'orcid': '0000-0003-2959-0617'}, {'id': 'Esterlis-Ilya', 'name': {'family': 'Esterlis', 'given': 'Ilya'}, 'orcid': '0000-0003-4775-9105'}, {'id': 'Demler-Eugene-A', 'name': {'family': 'Demler', 'given': 'Eugene'}, 'orcid': '0000-0002-2499-632X'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2023
DOI: 10.1103/physrevlett.130.147001
Twisted bilayer graphene (TBG) exhibits extremely low Fermi velocities for electrons, with the speed of sound surpassing the Fermi velocity. This regime enables the use of TBG for amplifying vibrational waves of the lattice through stimulated emission, following the same principles of operation of free-electron lasers. Our Letter proposes a lasing mechanism relying on the slow-electron bands to produce a coherent beam of acoustic phonons. We propose a device based on undulated electrons in TBG, which we dub the phaser. The device generates phonon beams in a terahertz (THz) frequency range, which can then be used to produce THz electromagnetic radiation. The ability to generate coherent phonons in solids breaks new ground in controlling quantum memories, probing quantum states, realizing nonequilibrium phases of matter, and designing new types of THz optical devices.https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/59pd4-ke593Optical Control of Slow Topological Electrons in Moiré Systems
https://authors.library.caltech.edu/records/s94x6-j8151
Authors: {'items': [{'id': 'Yang-Christopher', 'name': {'family': 'Yang', 'given': 'Christopher'}, 'orcid': '0000-0002-9462-9074'}, {'id': 'Esin-Iliya', 'name': {'family': 'Esin', 'given': 'Iliya'}, 'orcid': '0000-0003-2959-0617'}, {'id': 'Lewandowski-Cyprian', 'name': {'family': 'Lewandowski', 'given': 'Cyprian'}, 'orcid': '0000-0002-6944-9805'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2023
DOI: 10.1103/physrevlett.131.026901
<p>Floquet moiré materials possess optically-induced flat-electron bands with steady-states sensitive to drive parameters. Within this regime, we show that strong interaction screening and phonon bath coupling can overcome enhanced drive-induced heating. In twisted bilayer graphene (TBG) irradiated by a terahertz-frequency continuous circularly polarized laser, the extremely slow electronic states enable the drive to control the steady state occupation of high-Berry curvature electronic states. In particular, above a critical field amplitude, high-Berry-curvature states exhibit a slow regime where they decouple from acoustic phonons, allowing the drive to control the anomalous Hall response. Our work shows that the laser-induced control of topological and transport physics in Floquet TBG are measurable using experimentally available probes.</p>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/s94x6-j8151Energy transfer in random-matrix ensembles of Floquet Hamiltonians
https://authors.library.caltech.edu/records/pjtpz-rsh54
Authors: {'items': [{'name': {'family': 'Psaroudaki', 'given': 'Christina'}, 'orcid': '0000-0002-7073-6422'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2023
DOI: 10.1103/physrevb.108.064301
<p>We explore the statistical properties of energy transfer in ensembles of doubly driven random-matrix Floquet Hamiltonians based on universal symmetry arguments. The energy-pumping efficiency distribution P(E̅) is associated with the Hamiltonian parameter ensemble and the eigenvalue statistics of the Floquet operator. For specific Hamiltonian ensembles, P(E̅) undergoes a transition which cannot be associated with a symmetry breaking of the instantaneous Hamiltonian. The Floquet eigenvalue spacing distribution indicates the considered ensembles constitute generic nonintegrable Hamiltonian families. As a step towards Hamiltonian engineering, we develop a machine-learning classifier to understand the relative parameter importance in resulting high-conversion efficiency. We propose random Floquet Hamiltonians as a general framework to investigate frequency conversion effects in a class of generic dynamical processes beyond adiabatic pumps.</p>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/pjtpz-rsh54Probing localization properties of many-body Hamiltonians via an imaginary vector potential
https://authors.library.caltech.edu/records/za6mp-a9645
Authors: {'items': [{'id': "O'Brien-Liam", 'name': {'family': "O'Brien", 'given': 'Liam'}, 'orcid': '0000-0002-8603-1347'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}]}
Year: 2023
DOI: 10.1103/physrevb.108.184207
<p>Identifying and measuring the "localization length" in many-body systems in the vicinity of a many-body localization transition is difficult. Following Hatano and Nelson, a recent paper [S. Heußen, C. D. White, and G. Refael, <a href="http://dx.doi.org/10.1103/PhysRevB.103.064201">Phys. Rev. B <strong>103</strong>, 064201 (2021)</a>] introduced an "imaginary vector potential" to a disordered ring of interacting fermions, in order to define a many-body localization length (corresponding, in the noninteracting case, to the end-to-end Green's function of the Hermitian system). We extend these results, by connecting this localization length to the length scale appearing in the avalanche model of delocalization. We use this connection to derive the distribution of the localization length at the MBL transition, finding good agreement with our numerical observations. Our results demonstrate how a localization length defined as such probes the localization of the underlying ring, without the need to explicitly construct the l-bits.</p>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/za6mp-a9645Measurement-induced chirality: Diffusion and disorder
https://authors.library.caltech.edu/records/kghgg-2cw05
Authors: {'items': [{'id': 'Khor-Brian-J-J', 'name': {'family': 'Khor', 'given': 'Brian J. J.'}}, {'id': 'Wampler-Matthew', 'name': {'family': 'Wampler', 'given': 'Matthew'}, 'orcid': '0000-0001-6303-3561'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Klich-Israel', 'name': {'family': 'Klich', 'given': 'Israel'}, 'orcid': '0000-0002-8979-0170'}]}
Year: 2023
DOI: 10.1103/physrevb.108.214305
<p>Repeated quantum measurements can generate effective new nonequilibrium dynamics in matter. Here we combine such a measurement driven system with disorder. In particular, we investigate the diffusive behavior in the system and the effect of various types of disorder on the measurement induced chiral transport protocol. We begin by characterizing the diffusive behavior produced by the measurements themselves in a clean system. We then examine the edge flow of particles per measurement cycle for three different types of disorder: site dilution, lattice distortion, and disorder in on-site chemical potential. In the quantum Zeno limit, the effective descriptions for the disordered measurement system with lattice distortions and random on-site potential can be modeled as a classical stochastic model, and the overall effect of increasing these disorders induces a crossover from perfect flow to zero transport. On the other hand if vacancies are present in the lattice the flow of particles per measurement cycle undergoes a percolation phase transition from unity to zero with percolation threshold <i>p꜀ </i>≈ 0.26, with critical exponent <i>ν</i> ≈ 1.35. We also present numerical results away from Zeno limit and note that the overall effect of moving away from the Zeno effect is to reduce particle flow per cycle when the measurement frequency in our protocol is reduced.</p>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/kghgg-2cw05Universal transport in periodically driven systems without long-lived quasiparticles
https://authors.library.caltech.edu/records/ezez9-jyk89
Authors: {'items': [{'id': 'Esin-Iliya', 'name': {'family': 'Esin', 'given': 'Iliya'}, 'orcid': '0000-0003-2959-0617'}, {'id': 'Kuhlenkamp-Clemens', 'name': {'family': 'Kuhlenkamp', 'given': 'Clemens'}, 'orcid': '0000-0001-5529-4358'}, {'id': 'Refael-G', 'name': {'family': 'Refael', 'given': 'Gil'}}, {'id': 'Berg-Erez', 'name': {'family': 'Berg', 'given': 'Erez'}, 'orcid': '0000-0001-8956-3384'}, {'id': 'Rudner-Mark-S', 'name': {'family': 'Rudner', 'given': 'Mark S.'}, 'orcid': '0000-0002-5150-6234'}, {'id': 'Lindner-Netanel-H', 'name': {'family': 'Lindner', 'given': 'Netanel H.'}, 'orcid': '0000-0003-1879-3902'}]}
Year: 2024
DOI: 10.1103/physrevresearch.6.013094
<p>An intriguing regime of universal charge transport at high entropy density has been proposed for periodically driven interacting one-dimensional systems with Bloch bands separated by a large single-particle band gap. For weak interactions, a simple picture based on well-defined Floquet quasiparticles suggests that the system should host a quasisteady state current that depends only on the populations of the system's Floquet-Bloch bands and their associated quasienergy winding numbers. Here we show that such topological transport persists into the strongly interacting regime where the single-particle lifetime becomes shorter than the drive period. Analytically, we show that the value of the current is insensitive to interaction-induced band renormalizations and lifetime broadening when certain conditions are met by the system's nonequilibrium distribution function. We show that these conditions correspond to a quasisteady state. We support these predictions through numerical simulation of a system of strongly interacting fermions in a periodically modulated chain of Sachdev-Ye-Kitaev dots. Our paper establishes universal transport at high entropy density as a robust far from equilibrium topological phenomenon, which can be readily realized with cold atoms in optical lattices.</p>https://authors.library.caltech.eduhttps://authors.library.caltech.edu/records/ezez9-jyk89