[ { "id": "authors:5a1tw-xf975", "collection": "authors", "collection_id": "5a1tw-xf975", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220816-192424755", "type": "monograph", "title": "Vortex-enabled Andreev processes in quantum Hall-superconductor hybrids", "author": [ { "family_name": "Tang", "given_name": "Yuchen", "clpid": "Tang-Yuchen" }, { "family_name": "Knapp", "given_name": "Christina", "orcid": "0000-0002-5982-8107", "clpid": "Knapp-Christina" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "abstract": "Quantum Hall-superconductor heterostructures provide possible platforms for intrinsically fault-tolerant quantum computing. Motivated by several recent experiments that successfully integrated these phases, we investigate transport through a proximitized integer quantum Hall edge--paying particular attention to the impact of vortices in the superconductor. By examining the downstream conductance, we identify regimes in which sub-gap vortex levels mediate Andreev processes that would otherwise be frozen out in a vortex-free setup. Moreover, we show that at finite temperature, and in the limit of a large number of vortices, the downstream conductance can average to zero, indicating that the superconductor effectively behaves like a normal contact. Our results highlight the importance of considering vortices when using transport measurements to study superconducting correlations in quantum Hall-superconductor hybrids.", "doi": "10.48550/arXiv.2207.10687", "publisher": "arXiv", "publication_date": "2022-07-21" }, { "id": "authors:7btgy-p9d44", "collection": "authors", "collection_id": "7btgy-p9d44", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220816-183023896", "type": "monograph", "title": "Andreev reflection spectroscopy in strongly paired superconductors", "author": [ { "family_name": "Lewandowski", "given_name": "Cyprian", "orcid": "0000-0002-6944-9805", "clpid": "Lewandowski-Cyprian" }, { "family_name": "Lantagne-Hurtubise", "given_name": "\u00c9tienne", "orcid": "0000-0003-0417-6452", "clpid": "Lantagne-Hurtubise-\u00c9tienne" }, { "family_name": "Thomson", "given_name": "Alex", "orcid": "0000-0002-9938-5048", "clpid": "Thomson-Alex" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "abstract": "Motivated by recent experiments on low-carrier-density superconductors, including twisted multilayer graphene, we study signatures of the BCS to BEC evolution in Andreev reflection spectroscopy. We establish that in a standard quantum point contact geometry, Andreev reflection in a BEC superconductor is unable to mediate a zero-bias conductance beyond e\u00b2/h per lead channel. This bound is shown to result from a duality that links the sub-gap conductance of BCS and BEC superconductors. We then demonstrate that sharp signatures of BEC superconductivity, including perfect Andreev reflection, can be recovered by tunneling through a suitably designed potential well. We propose various tunneling spectroscopy setups to experimentally probe this recovery.", "doi": "10.48550/arXiv.2207.09494", "publisher": "arXiv", "publication_date": "2022-07-19" }, { "id": "authors:qqvh4-vrf77", "collection": "authors", "collection_id": "qqvh4-vrf77", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220524-180301852", "type": "monograph", "title": "Spin-Orbit Enhanced Superconductivity in Bernal Bilayer Graphene", "author": [ { "family_name": "Zhang", "given_name": "Yiran", "orcid": "0000-0002-8477-0074", "clpid": "Zhang-Yiran" }, { "family_name": "Polski", "given_name": "Robert", "orcid": "0000-0003-0887-8099", "clpid": "Polski-Robert-M" }, { "family_name": "Thomson", "given_name": "Alex", "orcid": "0000-0002-9938-5048", "clpid": "Thomson-Alex" }, { "family_name": "Lantagne-Hurtubise", "given_name": "\u00c9tienne", "orcid": "0000-0003-0417-6452", "clpid": "Lantagne-Hurtubise-\u00c9tienne" }, { "family_name": "Lewandowski", "given_name": "Cyprian", "orcid": "0000-0002-6944-9805", "clpid": "Lewandowski-Cyprian" }, { "family_name": "Zhou", "given_name": "Haoxin", "orcid": "0000-0003-1235-0035", "clpid": "Zhou-Haoxin" }, { "family_name": "Watanabe", "given_name": "Kenji", "orcid": "0000-0003-3701-8119", "clpid": "Watanabe-Kenji" }, { "family_name": "Taniguchi", "given_name": "Takashi", "orcid": "0000-0002-1467-3105", "clpid": "Taniguchi-Takashi" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "abstract": "In the presence of a large perpendicular electric field, Bernal-stacked bilayer graphene (BLG) features several broken-symmetry metallic phases as well as magnetic-field-induced superconductivity. The superconducting state is quite fragile, however, appearing only in a narrow window of density and with a maximum critical temperature T\ua700 \u2248 30~mK. Here, we show that placing monolayer tungsten diselenide (WSe\u2082) on BLG promotes Cooper pairing to an extraordinary degree: superconductivity appears at zero magnetic field, exhibits an order of magnitude enhancement in T\ua700, and occurs over a density range that is wider by a factor of eight. By mapping quantum oscillations in BLG-WSe\u2082 as a function of electric field and doping, we establish that superconductivity emerges throughout a region whose normal state is polarized, with two out of four spin-valley flavours predominantly populated. In-plane magnetic field measurements further reveal a striking dependence of the critical field on doping, with the Chandrasekhar-Clogston (Pauli) limit roughly obeyed on one end of the superconducting dome yet sharply violated on the other. Moreover, the superconductivity arises only for perpendicular electric fields that push BLG hole wavefunctions towards WSe\u2082 -- suggesting that proximity-induced (Ising) spin-orbit coupling plays a key role in enhancing the pairing. Our results pave the way for engineering robust, highly tunable, and ultra-clean graphene-based superconductors.", "doi": "10.48550/arXiv.2205.05087", "publisher": "arXiv", "publication_date": "2022-05-10" }, { "id": "authors:2jegc-73t42", "collection": "authors", "collection_id": "2jegc-73t42", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220428-212235605", "type": "monograph", "title": "Quantum spin liquids bootstrapped from Ising criticality in Rydberg arrays", "author": [ { "family_name": "Slagle", "given_name": "Kevin", "orcid": "0000-0002-8036-3447", "clpid": "Slagle-Kevin" }, { "family_name": "Liu", "given_name": "Yue", "orcid": "0000-0002-5965-0644", "clpid": "Liu-Yue" }, { "family_name": "Aasen", "given_name": "David", "orcid": "0000-0002-6552-488X", "clpid": "Aasen-David" }, { "family_name": "Pichler", "given_name": "Hannes", "orcid": "0000-0003-2144-536X", "clpid": "Pichler-Hannes" }, { "family_name": "Mong", "given_name": "Roger S. K.", "clpid": "Mong-Roger-S-K" }, { "family_name": "Chen", "given_name": "Xie", "orcid": "0000-0003-2215-2497", "clpid": "Chen-Xie" }, { "family_name": "Endres", "given_name": "Manuel", "orcid": "0000-0002-4461-224X", "clpid": "Endres-M" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "abstract": "Arrays of Rydberg atoms constitute a highly tunable, strongly interacting venue for the pursuit of exotic states of matter. We develop a new strategy for accessing a family of fractionalized phases known as quantum spin liquids in two-dimensional Rydberg arrays. We specifically use effective field theory methods to study arrays assembled from Rydberg chains tuned to an Ising phase transition that famously hosts emergent fermions propagating within each chain. This highly entangled starting point allows us to naturally access spin liquids familiar from Kitaev's honeycomb model, albeit from an entirely different framework. In particular, we argue that finite-range repulsive Rydberg interactions, which frustrate nearby symmetry-breaking orders, can enable coherent propagation of emergent fermions between the chains in which they were born. Delocalization of emergent fermions across the full two-dimensional Rydberg array yields a gapless Z2 spin liquid with a single massless Dirac cone. Here, the Rydberg occupation numbers exhibit universal power-law correlations that provide a straightforward experimental diagnostic of this phase. We further show that explicitly breaking symmetries perturbs the gapless spin liquid into gapped, topologically ordered descendants: Breaking lattice symmetries generates toric-code topological order, whereas introducing chirality generates non-Abelian Ising topological order. In the toric-code phase, we analytically construct microscopic incarnations of non-Abelian defects, which can be created and transported by dynamically controlling the atom positions in the array. Our work suggests that appropriately tuned Rydberg arrays provide a cold-atoms counterpart of solid-state 'Kitaev materials' and, more generally, spotlights a new angle for pursuing experimental platforms for Abelian and non-Abelian fractionalization.", "doi": "10.48550/arXiv.2204.00013", "publisher": "arXiv", "publication_date": "2022-03-31" }, { "id": "authors:n990w-e2f28", "collection": "authors", "collection_id": "n990w-e2f28", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220113-234609742", "type": "monograph", "title": "Ascendance of Superconductivity in Magic-Angle Graphene Multilayers", "author": [ { "family_name": "Zhang", "given_name": "Yiran", "orcid": "0000-0002-8477-0074", "clpid": "Zhang-Yiran" }, { "family_name": "Polski", "given_name": "Robert", "orcid": "0000-0003-0887-8099", "clpid": "Polski-Robert-M" }, { "family_name": "Lewandowski", "given_name": "Cyprian", "orcid": "0000-0002-6944-9805", "clpid": "Lewandowski-Cyprian" }, { "family_name": "Thomson", "given_name": "Alex", "orcid": "0000-0002-9938-5048", "clpid": "Thomson-Alex" }, { "family_name": "Peng", "given_name": "Yang", "orcid": "0000-0002-8868-2928", "clpid": "Peng-Yang" }, { "family_name": "Choi", "given_name": "Youngjoon", "clpid": "Choi-Youngjoon" }, { "family_name": "Kim", "given_name": "Hyunjin", "orcid": "0000-0001-9886-0487", "clpid": "Kim-Hyunjin" }, { "family_name": "Watanabe", "given_name": "Kenji", "orcid": "0000-0003-3701-8119", "clpid": "Watanabe-Kenji" }, { "family_name": "Taniguchi", "given_name": "Takashi", "orcid": "0000-0002-1467-3105", "clpid": "Taniguchi-Takashi" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "von Oppen", "given_name": "Felix", "orcid": "0000-0002-2537-7256", "clpid": "von-Oppen-Felix" }, { "family_name": "Refael", "given_name": "Gil", "clpid": "Refael-G" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "abstract": "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.", "doi": "10.48550/arXiv.2112.09270", "publisher": "arXiv", "publication_date": "2021-12-17" }, { "id": "authors:gnrr3-rdt94", "collection": "authors", "collection_id": "gnrr3-rdt94", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220113-182244311", "type": "monograph", "title": "Spin chains, defects, and quantum wires for the quantum-double edge", "author": [ { "family_name": "Albert", "given_name": "Victor V.", "orcid": "0000-0002-0335-9508", "clpid": "Albert-Victor-V" }, { "family_name": "Aasen", "given_name": "David", "orcid": "0000-0002-6552-488X", "clpid": "Aasen-David" }, { "family_name": "Xu", "given_name": "Wenqing", "clpid": "Xu-Wenqing-William" }, { "family_name": "Ji", "given_name": "Wenjie", "clpid": "Ji-Wenjie" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Preskill", "given_name": "John", "orcid": "0000-0002-2421-4762", "clpid": "Preskill-J" } ], "abstract": "Non-Abelian defects that bind Majorana or parafermion zero modes are prominent in several topological quantum computation schemes. Underpinning their established understanding is the quantum Ising spin chain, which can be recast as a fermionic model or viewed as a standalone effective theory for the surface-code edge -- both of which harbor non-Abelian defects. We generalize these notions by deriving an effective Ising-like spin chain describing the edge of quantum-double topological order. Relating Majorana and parafermion modes to anyonic strings, we introduce quantum-double generalizations of non-Abelian defects. We develop a way to embed finite-group valued qunits into those valued in continuous groups. Using this embedding, we provide a continuum description of the spin chain and recast its non-interacting part as a quantum wire via addition of a Wess-Zumino-Novikov-Witten term and non-Abelian bosonization.", "doi": "10.48550/arXiv.2111.12096", "publisher": "arXiv", "publication_date": "2021-11-23" }, { "id": "authors:sz595-h0961", "collection": "authors", "collection_id": "sz595-h0961", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220113-182215445", "type": "monograph", "title": "Spectroscopic Signatures of Strong Correlations and Unconventional Superconductivity in Twisted Trilayer Graphene", "author": [ { "family_name": "Kim", "given_name": "Hyunjin", "orcid": "0000-0001-9886-0487", "clpid": "Kim-Hyunjin" }, { "family_name": "Choi", "given_name": "Youngjoon", "clpid": "Choi-Youngjoon" }, { "family_name": "Lewandowski", "given_name": "Cyprian", "orcid": "0000-0002-6944-9805", "clpid": "Lewandowski-Cyprian" }, { "family_name": "Thomson", "given_name": "Alex", "orcid": "0000-0002-9938-5048", "clpid": "Thomson-Alex" }, { "family_name": "Zhang", "given_name": "Yiran", "orcid": "0000-0002-8477-0074", "clpid": "Zhang-Yiran" }, { "family_name": "Polski", "given_name": "Robert", "orcid": "0000-0003-0887-8099", "clpid": "Polski-Robert-M" }, { "family_name": "Watanabe", "given_name": "Kenji", "orcid": "0000-0003-3701-8119", "clpid": "Watanabe-Kenji" }, { "family_name": "Taniguchi", "given_name": "Takashi", "orcid": "0000-0002-1467-3105", "clpid": "Taniguchi-Takashi" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Nadj-Perge", "given_name": "Stevan", "orcid": "0000-0002-2394-9070", "clpid": "Nadj-Perge-S" } ], "abstract": "Magic-angle twisted trilayer graphene (MATTG) has emerged as a novel moir\u00e9 material that exhibits both strong electronic correlations and unconventional superconductivity. However, spectroscopic studies of its electronic properties are lacking, and the nature of superconductivity and the corresponding order parameter in this system remain elusive. Here we perform high-resolution scanning tunneling microscopy and spectroscopy of MATTG and reveal extensive regions of atomic reconstruction that favor mirror-symmetric stacking. In these regions, we observe a cascade of symmetry-breaking electronic transitions and doping-dependent band structure deformations similar to those realized in magic-angle bilayers, as expected theoretically given the commonality of flat bands. More strikingly, in a density window spanning two to three holes per moire unit cell, spectroscopic signatures of superconductivity are manifest as pronounced dips in the tunneling conductance at the Fermi level accompanied by coherence peaks that become gradually suppressed at elevated temperatures and magnetic fields. The observed evolution of the conductance with doping is consistent with a gate-tunable transition from a gapped to a nodal superconductor, which we show theoretically is compatible with a sharp transition from a Bardeen-Cooper-Schrieffer (BCS) to a Bose-Einstein condensation (BEC) superconductor with a nodal order parameter. Within this doping window, we also detect peak-dip-hump structures suggesting that superconductivity is driven by strong coupling to bosonic modes of MATTG. Our results pave the way for further understanding of superconductivity and correlated states in graphene-based moir\u00e9 structures beyond twisted bilayers, where unconventional superconductivity and nodal pairing were reported.", "doi": "10.48550/arXiv.2109.12127", "publisher": "arXiv", "publication_date": "2021-09-24" }, { "id": "authors:trrzm-8xw29", "collection": "authors", "collection_id": "trrzm-8xw29", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20220104-233139832", "type": "monograph", "title": "Thermal anyon interferometry in phonon-coupled Kitaev spin liquids", "author": [ { "family_name": "Klocke", "given_name": "Kai", "orcid": "0000-0002-9580-8509", "clpid": "Klocke-Kai" }, { "family_name": "Moore", "given_name": "Joel E.", "clpid": "Moore-Joel-E" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Hal\u00e1sz", "given_name": "G\u00e1bor B.", "clpid": "Hal\u00e1sz-G\u00e1bor-B" } ], "abstract": "Recent theoretical studies inspired by experiments on the Kitaev magnet \u03b1-RuCl\u2083 highlight the nontrivial impact of phonons on the thermal Hall conductivity of chiral topological phases. Here we introduce mixed mesoscopic-macroscopic devices that allow refined thermal-transport probes of non-Abelian spin liquids with Ising topological order. These devices feature a quantum-coherent mesoscopic region with negligible phonon conductance, flanked by macroscopic lobes that facilitate efficient thermalization between chiral Majorana edge modes and bulk phonons. We show that our devices enable (i) accurate determination of the quantized thermal Hall conductivity, (ii) identification of non-Abelian Ising anyons via the temperature dependence of the thermal conductance, and most interestingly (iii) single-anyon detection through heat-based anyon interferometry. Analogous results apply broadly to phonon-coupled chiral topological orders.", "doi": "10.48550/arXiv.2105.05869", "publisher": "arXiv", "publication_date": "2021-05-12" }, { "id": "authors:wec65-tmt62", "collection": "authors", "collection_id": "wec65-tmt62", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200727-084626398", "type": "monograph", "title": "Survival of the fractional Josephson effect in time-reversal-invariant topological superconductors", "author": [ { "family_name": "Knapp", "given_name": "Christina", "orcid": "0000-0002-5982-8107", "clpid": "Knapp-Christina" }, { "family_name": "Chew", "given_name": "Aaron", "orcid": "0000-0003-0448-6215", "clpid": "Chew-Aaron" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" } ], "abstract": "Time-reversal-invariant topological superconductor (TRITOPS) wires host Majorana Kramers pairs that have been predicted to mediate a fractional Josephson effect with 4\u03c0 periodicity in the superconducting phase difference. We explore the TRITOPS fractional Josephson effect in the presence of time-dependent `local mixing' perturbations that instantaneously preserve time-reversal symmetry. Specifically, we show that just as such couplings render braiding of Majorana Kramers pairs non-universal, the Josephson current becomes either aperiodic or 2\u03c0-periodic (depending on conditions that we quantify) unless the phase difference is swept sufficiently quickly. We further analyze topological superconductors with T\u00b2 = +1 time-reversal symmetry and reveal a rich interplay between interactions and local mixing that can be experimentally probed in nanowire arrays.", "doi": "10.48550/arXiv.2006.10772", "publisher": "arXiv", "publication_date": "2020-06-18" }, { "id": "authors:s5y49-bpb05", "collection": "authors", "collection_id": "s5y49-bpb05", "cite_using_url": "https://resolver.caltech.edu/CaltechAUTHORS:20200225-105137997", "type": "monograph", "title": "Engineering a robust quantum spin Hall state in graphene via adatom deposition", "author": [ { "family_name": "Weeks", "given_name": "Conan", "clpid": "Weeks-C" }, { "family_name": "Hu", "given_name": "Jun", "clpid": "Hu-Jun" }, { "family_name": "Alicea", "given_name": "Jason", "orcid": "0000-0001-9979-3423", "clpid": "Alicea-J" }, { "family_name": "Franz", "given_name": "Marcel", "clpid": "Franz-M" }, { "family_name": "Wu", "given_name": "Ruqian", "clpid": "Wu-Ruqian" } ], "abstract": "The 2007 discovery of quantized conductance in HgTe quantum wells delivered the field of topological insulators (TIs) its first experimental confirmation. While many three-dimensional TIs have since been identified, HgTe remains the only known two-dimensional system in this class. Difficulty fabricating HgTe quantum wells has, moreover, hampered their widespread use. With the goal of breaking this logjam we provide a blueprint for stabilizing a robust TI state in a more readily available two-dimensional material---graphene. Using symmetry arguments, density functional theory, and tight-binding simulations, we predict that graphene endowed with certain heavy adatoms realizes a TI with substantial band gap. For indium and thallium, our most promising adatom candidates, a modest 6% coverage produces an estimated gap near 80K and 240K, respectively, which should be detectable in transport or spectroscopic measurements. Engineering such a robust topological phase in graphene could pave the way for a new generation of devices for spintronics, ultra-low-dissipation electronics and quantum information processing.", "doi": "10.48550/arXiv.1104.3282", "publisher": "PHYS.REV.X", "publication_date": "2011-04-17" } ]