Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session U55: Topological Superconductors in More Than One DimensionFocus

Hide Abstracts 
Sponsoring Units: DCMP Chair: Daniel Agterberg, University of Wisconsin  Milwaukee Room: Mile High Ballroom 2B 
Thursday, March 5, 2020 2:30PM  3:06PM 
U55.00001: Superconductivity without timereversal or inversion symmetries Invited Speaker: Daniel Agterberg To ensure a superconducting instability, key symmetries are required. In three dimensions (3D), these are timereversal (T) and inversion (I) symmetries. In two dimensions, T and I are joined by TM_{z} and IM_{z} symmetries where M_{z} is a mirror reflection through the basal plane. Here we discuss unusual physics that arises when one or more of these key symmetries are broken. In particular, in 3D, we show that spontaneously breaking T symmetry allows for topologically protected nodal Bogoliubov Fermi surfaces and apply this idea to URu_{2}Si_{2} and Sr_{2}RuO_{4}. In 2D, we develop an energetic and topological superconductor classification in the unfamiliar situation that both T and I symmetreis are absent. We apply this to Ising superconductors with inplane magnetic fields and monolayer FeSe coexisting with antiferromagnetic order. 
Thursday, March 5, 2020 3:06PM  3:18PM 
U55.00002: Supercurrentinduced Majorana bound states in a planar geometry AndrĂ© Melo, Sebastian Rubbert, Anton Akhmerov We propose a new setup for creating Majorana bound states in a twodimensional electron gas Josephson junction. Our proposal relies exclusively on a supercurrent parallel to the junction as a mechanism of breaking timereversal symmetry. We show that combined with spinorbit coupling, supercurrents induce a Zeemanlike spin splitting. Further, we identify a new conserved quantitychargemomentum paritythat prevents the opening of the topological gap by the supercurrent in a straight Josephson junction. We propose breaking this conservation law by adding a third superconductor, introducing a periodic potential, or making the junction zigzagshaped. By comparing the topological phase diagrams and practical limitations of these systems we identify the zigzagshaped junction as the most promising option. 
Thursday, March 5, 2020 3:18PM  3:30PM 
U55.00003: Dissipative chiral superconductors in 3D Meng Hua, Lingyu Yang, Jeffrey Teo Topological band theories that describe insulators, superconductors and (semi)metals are conventionally classified according to the AltlandZirnbauer classification based on the presence or absence of local timereversal and particlehole symmetries. More recently, there are theoretical generalizations that incorporate nonlocal magnetic space group symmetries. There are more exotic combined antiunitary spatial symmetries that involve particlehole conjugation and may be allowed in a nonHermitian system. In this talk, we focus on the classification, model realization and topologicalindex characterization of dissipative topological superconductors in 3D and the corresponding dissipative chiral Majorana fermion on the boundary surface. 
Thursday, March 5, 2020 3:30PM  3:42PM 
U55.00004: Topological Skyrmion Phases of Matter Ashley Cook We introduce twodimensional topological phases of matter defined by nontrivial homotopy groups into the literature, characterized either by a single Skyrmion number, known as the chiral topological Skymion insulator, or a pair of Skyrmion numbers, known as the helical topological Skyrmion insulator, which generalize and extend the concepts of the Chern insulator and quantum spin Hall insulator, respectively. We show each topological phase of matter is protected by a combination of a mirror symmetry and a generalized particlehole symmetry equal to the product of particlehole symmetry and spatial inversion symmetry. Despite these phases being protected in part by crystalline point group symmetries, the phases introduced here are very different from all others known: we characterize three kinds of phase transitions by which a Skyrmion number can change. One kind of topological phase transition occurs without the closing of energy gaps, which has important consequences for study of topologically nontrivial phases of matter. We find that each phase is realized in a tightbinding model relevant to Sr2RuO4 and discuss experimental realization given that the chiral topological Skyrmion insulator phase is realized for a parameter set used to characterize Sr2RuO4. 
Thursday, March 5, 2020 3:42PM  3:54PM 
U55.00005: TripletSuperconductivity in TripleBand Crossings GiBaik Sim, Moon Jip Park, SungBin Lee In this talk, we will introduce the triplet superconductivity in the newly discovered form of the topological semimetal, where the electrons with pseudospin J=1 form tripleband crossings. The peculiar property of J=1 electrons is that Fermi statistics rules out onsite spin singlet pairing. Performing the exact decoupling of onsite electron interactions into pairing channels, we adopt the Landau theory of spintriplet pairings and study the Landau free energy functional to plot out the global phase diagram. We find two distinct phases; (i) timereversal symmetric (Sz) state, (ii) timereversal broken (Sx + i Sy) state. Remarkably, both of these states have gapless Bogoliubov quasiparticles and furthermore have topological invariants for each nodal line or Bogoliubov Fermi surface. 
Thursday, March 5, 2020 3:54PM  4:06PM 
U55.00006: Higherorder topological superconductor in ${\mathcal P}, {\mathcal T}$odd quadrupolar Dirac metal Bitan Roy Presence or absence of certain symmetries in the normal state (NS) also plays important role in determining the symmetry of the Cooper pairs. We here show that two and threedimensional Dirac metals, realized by doping parity (${\mathcal P}$) and timereversal (${\mathcal T}$) odd topologically trivial Dirac insulators, sustain a local or interunit cell pairing that assumes the form of a timereversal odd and mixed parity (due to the absence of ${\mathcal T}$ and ${\mathcal P}$ in the NS, respectively) pairing around the Fermi surface. When the NS additionally breaks discrete fourfold ($C_4$) symmetry (yielding a ${\mathcal P}$, ${\mathcal T}$odd, quadrupolar Dirac metal), the system gives birth to a higherorder $p+id$ pairing, hosting corner (in $d=2$) or hinge (in $d=3$) modes of codimension $d_c=2$ of Majorana fermions. While the $p$wave component stems from the Dirac nature of quasiparticles in the NS, appearance of the $d$wave component is solely attributed to the lack of $C_4$ symmetry, as its restoration produces $p+is$ pairing. 
Thursday, March 5, 2020 4:06PM  4:18PM 
U55.00007: Refined symmetry indicators for topological superconductors in all space groups Seishiro Ono, Hoi Chun Po, Haruki Watanabe Topological superconductors are exotic phases of matter featuring robust surface states that could be leveraged for topological quantum computation. A useful guiding principle for the search of topological superconductors is to relate the topological invariants with the behavior of the pairing order parameter on the normalstate Fermi surfaces. The existing formulas, however, become inadequate for the prediction of the recently proposed classes of topological crystalline superconductors. 
Thursday, March 5, 2020 4:18PM  4:30PM 
U55.00008: Emergent spacetime and gravitational NiehYan anomaly in chiral Weyl superfluids and superconductors Jaakko Nissinen Momentum transport in topological Weyl superfluids (and superconductors) is anomalous in the presence of textures and superflow. Using the semiclassical approximation and gradient expansion, the gauge and Galilean symmetries of the system induce via the superfluid hydrodynamics an emergent "RiemannCartan" spacetime with torsion and curvature for the lowenergy Weyl quasiparticles. Furthermore, the background exhibits local conservation laws corresponding to emergent quasirelativistic Lorentz symmetry. We show that the momentum anomaly can be given a consistent interpretation as the chiral NiehYan gravitational anomaly experienced by Weyl fermions on the emergent curved spacetime. The coefficient of this anomaly term is not universally quantized and seems to be determined by the underlying nonrelativistic Fermiliquid and Galilean symmetries. Finally, the connection and extension of the emergent spacetime to finite temperature corrections and thermal effects will be discussed. 
Thursday, March 5, 2020 4:30PM  4:42PM 
U55.00009: Weylsuperconductor phases in the multilayer model of Weyl semimetals and superconductors Ryota Nakai, Kentaro Nomura We study the superconducting proximity effect in the bulk of Weyl semimetals by considering a multilayer structure consisting of alternating Weylsemimetal and superconductor (WSMSC) layers. Our model realizes Weylsuperconductor phases with 2 or 4 nodes of the Majorana fermion, and (2d) topologicalsuperconductor phases characterized by halfoddinteger and integer Chern numbers. We found that potential barriers at the interface and/or mismatch of the Fermi velocity favor topologicalsuperconductor phases with halfodd integer Chern numbers, while Weylsuperconductor phases with 4 nodes and topologicalsuperconductor phases with integer Chern numbers are realized when the Fermi velocity coincides. Topologicalsuperconductor phases are characterized by the quantization of the thermal Hall conductivity, and Weylsuperconductor phases by continuously varying thermal Hall conductivity determined by the position of nodes. 
Thursday, March 5, 2020 4:42PM  4:54PM 
U55.00010: Edge current and orbital angular momentum of chiral superfluids revisited Wenxing Nie, Wen Huang, Hong Yao Cooper pairs in chiral superfluids carry quantized units of orbital angular momentum (OAM). Various predictions of the total OAM of a chiral superfluid differ by several orders of magnitude. These constitute the socalled angular momentum paradox. Following several previous studies, we substantiate the semiclassical Bogoliubovde Gennes theory of the edge current and OAM in twodimensional chiral superfluids in the BCS limit. The analysis provides a simple intuitive understanding for the vanishing of OAM in a nonpwave chiral superfluid (such as d+id) confined by a rigid potential. When generalized to anisotropic chiral superconductors and threedimensional (3D) chiral superfluids, the theory similarly returns an accurate description. We will also present a numerical study of the chiral phases in the BEC limit, where the OAM density is found to vanish in the bulk and arise purely from the boundary effects. 
Thursday, March 5, 2020 4:54PM  5:06PM 
U55.00011: Vortices in a Monopole Superconducting Weyl Semimetal ShuPing Lee, Canon Sun, Yi Li A monopole superconductor is a novel topological phase of matter with topologically protected gap nodes that result from the nontrivial Berry phase structure of Cooper pairs. In this work we study the zeroenergy vortex bound states in a model of a monopole superconductor based on a timereversal broken Weyl semimetal with proximityinduced superconductivity. The zero modes exhibit a nontrivial phase winding in real space as a result of the nontrivial winding of the order parameter in momentum space. By mapping the Hamiltonian to the $(1+1)$d Dirac Hamiltonian, it is shown that the zero modes, analogous to the JackiwRebbi mode, are protected by the index theorem. 
Thursday, March 5, 2020 5:06PM  5:18PM 
U55.00012: Majorana Kramers Pairs in HigherOrder Topological Insulators ChenHsuan Hsu, Peter Stano, Jelena Klinovaja, Daniel Loss We propose a tunefree scheme to realize Majorana bound states using higherorder topological insulators [1]. When two hinges of a higherorder topological insulator nanowire are brought into the proximity of an swave superconductor, two types of pairings arise, one being local (intrahinge) pairing and the other nonlocal (interhinge) pairing. We find that, the competition between these pairings leads to a topological phase transition. The energy band is inverted in the regime where the nonlocal pairing dominates over the local one, leading to the formation of a Kramers pair of Majorana bound states at each end of the nanowire. We show that this topological condition can be fulfilled in the presence of moderate electronelectron interactions, without finetuning system parameters such as external magnetic fields. 
Thursday, March 5, 2020 5:18PM  5:30PM 
U55.00013: TopologyBounded Superfluid Weight in Twisted Bilayer Graphene Fang Xie, Zhida Song, Biao Lian, Andrei Bernevig We derive the superfluid weight (phase stiffness) of the TBLG superconducting flat bands with a uniform pairing, and show that it can be expressed as an integral of the FubiniStudy metric of the flat bands. This mirrors results [1] already obtained for nonzero Chern number bands even though the TBLG flat bands have zero Chern number. We further show the metric integral is lower bounded by the topological C2zT Wilson loop winding number of the TBLG flat bands, which renders the superfluid weight has a topological lower bound proportional to the pairing gap. In contrast, trivial flat bands have a zero superfluid weight. The superfluid weight is crucial in determining the BKT transition temperature of the superconductor. Based on the transition temperature measured in TBLG experiments, we estimate the topological contribution of the superfluid weight in TBLG. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2024 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700