Article records
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A Caltech Library Repository Feedhttp://www.rssboard.org/rss-specificationpython-feedgenenWed, 29 Nov 2023 17:16:39 +0000Antisymmetric linear magnetoresistance and the planar Hall effect
https://resolver.caltech.edu/CaltechAUTHORS:20190624-074905872
Authors: Wang, Yishu; Lee, Patrick A.; Silevitch, D. M.; Gómez, F.; Cooper, S. E.; Ren, Y.; Yan, J.-Q.; Mandrus, D.; Rosenbaum, T. F.; Feng, Yejun
Year: 2020
DOI: 10.1038/s41467-019-14057-6
PMCID: PMC6954222
The phenomena of antisymmetric magnetoresistance and the planar Hall effect are deeply entwined with ferromagnetism. The intrinsic magnetization of the ordered state permits these unusual and rarely observed manifestations of Onsager's theorem when time reversal symmetry is broken at zero applied field. Here we study two classes of ferromagnetic materials, rare-earth magnets with high intrinsic coercivity and antiferromagnetic pyrochlores with strongly-pinned ferromagnetic domain walls, which both exhibit antisymmetric magnetoresistive behavior. By mapping out the peculiar angular variation of the antisymmetric galvanomagnetic response with respect to the relative alignments of the magnetization, magnetic field, and electrical current, we experimentally distinguish two distinct underlying microscopic mechanisms: namely, spin-dependent scattering of a Zeeman-shifted Fermi surface and anomalous electron velocities. Our work demonstrates that the anomalous electron velocity physics typically associated with the anomalous Hall effect is prevalent beyond the ρ_(xy)(H_z) channel, and should be understood as a part of the general galvanomagnetic behavior.https://authors.library.caltech.edu/records/r6nmj-zpq39Topological superconductivity in nanowires proximate to a diffusive superconductor–magnetic-insulator bilayer
https://resolver.caltech.edu/CaltechAUTHORS:20210421-103423569
Authors: Khindanov, Aleksei; Alicea, Jason; Lee, Patrick; Cole, William S.; Antipov, Andrey E.
Year: 2021
DOI: 10.1103/physrevb.103.134506
We study semiconductor nanowires coupled to a bilayer of a disordered superconductor and a magnetic insulator, motivated by recent experiments reporting possible Majorana-zero-mode signatures in related architectures. Specifically, we pursue a quasiclassical Usadel equation approach that treats superconductivity in the bilayer self-consistently in the presence of spin-orbit scattering, magnetic-impurity scattering, and Zeeman splitting induced by both the magnetic insulator and a supplemental applied field. Within this framework we explore prospects for engineering topological superconductivity in a nanowire proximate to the bilayer. We find that a magnetic-insulator-induced Zeeman splitting, mediated through the superconductor alone, cannot induce a topological phase since the destruction of superconductivity (i.e., Clogston limit) preempts the required regime in which the nanowire's Zeeman energy exceeds the induced pairing strength. However, this Zeeman splitting does reduce the critical applied field needed to access the topological phase transition, with fields antiparallel to the magnetization of the magnetic insulator having an optimal effect. Finally, we show that magnetic-impurity scattering degrades the topological phase, and spin-orbit scattering, if present in the superconductor, pushes the Clogston limit to higher fields yet simultaneously increases the critical applied field strength.https://authors.library.caltech.edu/records/gxma1-b2m80A continuous metal-insulator transition driven by spin correlations
https://resolver.caltech.edu/CaltechAUTHORS:20201111-082624574
Authors: Feng, Yejun; Wang, Yishu; Silevitch, D. M.; Cooper, S. E.; Mandrus, D.; Lee, Patrick A.; Rosenbaum, T. F.
Year: 2021
DOI: 10.1038/s41467-021-23039-6
PMCID: PMC8119431
While Mott insulators induced by Coulomb interactions are a well-recognized class of metal-insulator transitions, insulators purely driven by spin correlations are much less common, as the reduced energy scale often invites competition from other degrees of freedom. Here, we demonstrate a clean example of a spin-correlation-driven metal-insulator transition in the all-in-all-out pyrochlore antiferromagnet Cd₂Os₂O₇, where the lattice symmetry is preserved by the antiferromagnetism. After the antisymmetric linear magnetoresistance from conductive, ferromagnetic domain walls is removed experimentally, the bulk Hall coefficient reveals four Fermi surfaces of both electron and hole types, sequentially departing the Fermi level with decreasing temperature below the Néel temperature, T_N = 227 K. In Cd₂Os₂O₇, the charge gap of a continuous metal-insulator transition opens only at T ~ 10 K << T_N. The insulating mechanism parallels the Slater picture, but without a folded Brillouin zone, and contrasts sharply with Mott insulators and spin density waves, where the electronic gap opens above and at T_N, respectively.https://authors.library.caltech.edu/records/9w247-4s422Detection of collective modes in unconventional superconductors using tunneling spectroscopy
https://authors.library.caltech.edu/records/q6zf6-h5c46
Authors: Lee, Patrick A.; Steiner, Jacob F.
Year: 2023
DOI: 10.1103/physrevb.108.174503
<p>We propose using tunneling spectroscopy with a superconducting electrode to probe the collective modes of unconventional superconductors. The modes are predicted to appear as peaks in <i>dI/dV</i> at voltages given by <i>eV</i> = <i>ωᵢ</i>/2 where <i>ωᵢ</i> denotes the mode frequencies. This may prove to be a powerful tool to investigate the pairing symmetry of unconventional superconductors. The peaks associated with the collective modes appear at fourth order in the single-particle tunneling-matrix element. At the same fourth order, multiple Andreev reflection (MAR) leads to peaks at voltage equal to the energy gaps, which, in BCS superconductors, coincides with the expected position of the amplitude (Higgs) mode. The peaks stemming from the collective modes of unconventional superconductors do not suffer from this coincidence. For scanning tunneling microscopes, we estimate that the magnitude of the collective mode contribution is smaller than the MAR contribution by the ratio of the energy gap to the Fermi energy. Moreover, there is no access to the mode dispersion. Conversely, for planar tunnel junctions the collective mode peak is expected to dominate over the MAR peak, and the mode dispersion can be measured. We discuss systems where the search for such collective modes is promising.</p>https://authors.library.caltech.edu/records/q6zf6-h5c46