Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L47: Superconductivity Theory: Mainly topological effectsLive
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Sponsoring Units: DCMP Chair: Keith Taddei, Oak Ridge National Lab |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L47.00001: Strongly parity-mixed superconductivity in the Rashba-Hubbard model Kosuke Nogaki, Youichi Yanase Recently, artificial superlattices containing strongly correlated electron systems, such as CeCoIn5/YbCoIn5, have been fabricated [1]. Rashba-type antisymmetric spin-orbit coupling (ASOC) arises from polar inversion symmetry breaking at the interface of heterostructures. Unique superconducting phases are expected to be realized there owing to the interplay of two-dimensional magnetic fluctuations and Rashba ASOC. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L47.00002: Magnetic response and topology of a staggered-Rashba superconductor Mark Fischer, Anastasiia Skurativska, Manfred W Sigrist, Eric Schertenleib The presence or absence of a center of inversion is a standard classifying property of superconducting materials: If the system possesses inversion, spin-singlet and spin-triplet order parameters are distinct by symmetry and can be distinguished experimentally through their magnetic response. In non-centrosymmetric systems, on the other hand, the two order parameters can mix and the magnetic response is inconclusive. Still, since a dominant spin-triplet order parameter can be a topological superconductor, it can be identified through its edge states. In our work, we examine the situation, where inversion is broken locally in a sublattice, but retained globally. In particular, we investigate the magnetic response and possible topological superconducting states for a system consisting of layers with alternating Rashba spin-orbit coupling in the z direction and focus on the situation of large spin-orbit coupling. In this case, the system shows signs of non-centrosymmetricity even for sizable hopping in the z direction, in other words in the three-dimensional limit. This opens the way to design new types of superconducting order parameters which are robust against magnetism. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Live |
L47.00003: Quasiperiodic criticality and spin-triplet superconductivity in superconductor-antiferromagnet moire patterns Maryam Khosravian, Jose Lado Quasiperiodicity has long been known to be a potential platform to explore exotic phenomena, |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L47.00004: Evidence of pair-density wave in doping Kitaev spin liquid on the honeycomb lattice Cheng Peng, Yi-Fan Jiang, Thomas Devereaux, Hong-Chen Jiang Pair-density wave (PDW) is a novel superconducting (SC) state in which the SC order parameter varies periodically in real space such that its spatial average vanishes. Whether the PDW state can be induced by doping certain quantum spin liquid (QSL) remains an open question. We study the effects of doping the Kitaev spin liquid on honeycomb lattice using density-matrix renormalization group. The effect of hole doping is studied within the t-JK model on a three-leg cylinder where the spins interact via the bond-directional interaction JK. Upon light doping, we find that the ground state of the system has quasi-long-range charge-density-wave correlations but short-range single-particle correlations. The dominant pairing channel is the even-parity superconducting pair-pair correlation with d-wave-like symmetry, which oscillates in sign as a function of separation with a period equal to that of the spin-density wave and two times the charge-density wave. Although these correlations fall rapidly at long distances, this is never-the-less the first example where a PDW is the strongest SC order on a bipartite lattice. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L47.00005: Surface-acoustic-wave-induced unconventional superconducting pairing Viktoriia Kornich, Bjoern Trauzettel Unconventional superconductivity is usually associated with symmetry breaking in the system. In this work, we consider the effective electron-electron pairing due to an applied surface acosutic wave (SAW) in analogy to phonon-mediated electron-electron interaction in conventional superconductors. Here, however, SAW breaks time and spatial translation symmetries and has externally defined properties such as period and shape. We study the symmetries of the possible SAW-induced order parameters, showing that odd-frequency spin-singlet odd-parity or odd-frequency spin-triplet even-parity order parameters can occur. We suggest other methods of how to engineer the symmetries of the order parameters using SAWs and the applications of such setups in quantum technologies, e.g. braiding of Majorana bound states or long-range coupling of semiconductor qubits. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L47.00006: Chirality polarizations and proof of spectral bulk-boundary correspondence Akito Daido, Youichi Yanase Surface physics determined by bulk properties is attracting attention these days. An important context is the electric polarization, where the surface charge is the bulk property modulo a quantum. A difference from the topological bulk-boundary correspondence (BBC) is that surface chage can take continuos values. Such a correspondence of continuous quantities in the bulk and the surface has not been fully explored. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L47.00007: Possible Mechanisms to Stabilize Nematic Superconductivity Adil Amin, Daniel Agterberg The discovery of two superconducting transitions in UPt3 opened many new questions. The most pressing of which was the stablitiy of the A nematic state when weak-coupling theories predicted that the time-reversal symmetry breaking state is stable across the whole phase diagram. In this talk, we present a mechanism where a generalized spin fluctuation feedback effect can stabilize the nematic state by coupling superconductivity to electronic fluctuations [1]. This effect provides a unifying explanation for the existence of nematic states in the heavy fermions which show two transitions while additonally constraining the possible order parameters. We shall also connect this to reports of nematic superconductivity in twisted bilayer graphene. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L47.00008: Cavity-assisted superconductivity in low-dimensional systems Dushko Kuzmanovski, Ruben Seoane Souto, Alexander Balatsky Coupling to vacuum fluctuations of an electromagnetic cavity mode can significantly enhance the electron-electron pairing. The enhancement is due to significant compression of the cavity field far below the free-space diffraction limit. We consider low-dimensional systems, such as helical one-dimensional edge modes on a topological material or discrete energy levels in quantum dots coupled via a cavity mode with proper polarization. Applying an Eliashberg-type self-consistent approximation, we investigate the resulting superconducting pairing in various unconventional channels, including both a finite center-of-mass momentum, as well as dynamical superconducting pairing. We explore signatures in the single-particle excitation spectrum, spin response, as well as polariton collective excitation. The platform enables exploration of optical control of superconducting states, enhanced charge transport, polariton superconductivity, and cavity BEC transition. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L47.00009: For room-temperature superconductivity, abruptly diverging Tc over a transition pressure, 225 GPa, explained by Brinkman-Rice picture Hyun-Tak Kim For discovered room-temperature superconductivity of 287.7±12 K at 267±10 GPa in a H-S-C compound, Tc-discontinuity around Ptransition=225 GPa and Tc-divergence over Ptransition were observed [1]. Explaining Tc-divergence is a core problem for the mechanism of room-temperature superconductivity. ~~The Tc-divergence results from 3D-density of states, N(0)*, with diverging behavior of m* induced by a large correlation strength of κBR=U/Uc near ρ≈1 [2]. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L47.00010: Ising Superconductivity and Magnetism in NbSe2 Darshana Wickramaratne, Sergii Khmelevskyi, Daniel Agterberg, Igor Mazin We use density-functional theory (DFT) calculations to quantitatively address the superconducting properties of bulk and monolayer NbSe2 [1]. We demonstrate that NbSe2 is close to a ferromagnetic instability, and analyze our results in the context of experimental measurements of the spin susceptibility in NbSe2. We show how this magnetic instability, which is pronounced in a single monolayer, can enable sizable singlet-triplet mixing of the superconducting order parameter, contrary to contemporary considerations of the pairing symmetry in monolayer NbSe2, Our calculations also enable a quantitative description of the large anisotropy of the superconducting critical field, using DFT calculations of monolayer NbSe2 in the normal state. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L47.00011: Density wave and topological superconductivity in the magic-angle-twisted bilayer-graphene Ming Zhang The model dependence in the study of the magic-angle twisted bilayer-graphene is an important issue in the research area.It has been argued previously that the two-band tight-binding model (per spin and valley) cannot serve as a start point for succeeding studies as it cannot correctly describe the topological aspect of the continuum-theory model near the Dirac nodes in the mini Brillouin zone. For this purpose, we adopt the faithful TB model [Phys. Rev. B 99, 195455 (2019)] with five bands as our start point, which is further equipped with extended Hubbard interactions. Then after systematic randomphase-approximation based calculations, we study the electron instabilities of this model, including the density wave and superconductivity, near the van Hove singularity. The results are highly similar to the results of our previous study [arXiv:2003.09513] adopting the two-band TB modelmodel, with the reason lying in that both models share the same symmetry and Fermi-surface nesting character near the |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L47.00012: Spectroscopic Evidence for a Spin- and Valley-Polarized Metallic State in a Nonmagic-AngleTwisted Bilayer Graphene Chen Lu In the magic-angle twisted bilayer graphene (MATBG), strong electron−electron (e−e) correlations caused by the band-flattening lead to many exotic quantum phases such as superconductivity, correlated insulator, ferromagnetism, and quantum anomalous Hall effects, when its low-energy van Hove singularities (VHSs) are partially filled. We collaborated with the experimental group of Prof. Lin He from the Beijing Normal University on the twisted bilayer-graphene. The STM observations of He’s group showed that the 1.49o-twisted bilayer graphene would experience a phase transition at low temperature when the one van Hove peak would be split into four peaks. Simultaneously, the spatial symmetry of electronic states around the split VHSs is broken by the e−e correlation. Our analysis based on the continuum model suggests that such a one-to-four split of the VHS originates from the formation of an interaction-driven spin-valley-polarized metallic state near the VHS, which is a symmetry-breaking phase that has not been identified in the MA-TBG or in other systems. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L47.00013: T-J model on Penrose lattice Yubo LIU In recent years, quasicrystals have attracted extensive research. They lack translational symmetry, but have rotational symmetry that does not exist in crystals. Penrose lattice is a typical two-dimensional quasicrystalline structure. We studied the t-j model on the penrose lattice. First, we use the mean-field method to process the Hamiltonian in real space, and then self-consistently solve the BdG equation. In the end, we got the result that the ground state of the s wave generally has the lowest energy under different doping conditions, and these ground states satisfy Anderson's theorem. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L47.00014: Oxide Room Temperature Superconductivity At Ambient Pressure: Computations and Experimental Verifications Onyedinachi-Paul Isikaku-Ironkwe Achieving room temperature superconductivity (RTS), at atmospheric pressure in a material of known chemical composition, is regarded as the Holy Grail of condensed matter Physics. Recently, RTS was reported in a carbonaceous sulphur hydride of unknown composition at 2.6 million atmospheres pressure. In our quest to understand superconductivity in oxides, we have developed a Periodic Table based model called MSCD Framework for superconductors. We have used this model to design new high temperature superconductors (HTSCs), as reported in APS March Meetings (2016, 2018). We have also created new design algorithms and architectures that can host HTSCs beyond 160K in oxides, with six to seven elements. |
Wednesday, March 17, 2021 10:48AM - 11:00AM Live |
L47.00015: Finding exotic superconducting pairing in topological semimetals Paramita Dutta, Fariborz Parhizgar, Annica M Black-Schaffer We explore the possibility of exotic superconducting pairing in topological semimetals. The topology and the associated symmetries of the semimetals result in a unique electronic band structure, which affects the superconducting gap structure and pair amplitude. In addition to the conventional spin-singlet even-frequency pairing it is possible to find odd-frequency spin-triplet pairing and also pairing with higher intrinsic angular momentum. We also investigate possible experimental probes which can distinguish the signatures of the exotic pairing. |
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