Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session F43: Dirac and Weyl Semimetal: 3D to 2D and New FrontiersFocus
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Sponsoring Units: DMP Chair: Yujin Cho, Lawrence Livermore National Laboratory Room: Room 317 |
Tuesday, March 7, 2023 8:00AM - 8:36AM |
F43.00001: Quasi-symmetry protected topology in semi-metal Invited Speaker: Philip J Moll The crystal symmetry dictates the type of topological band structures it may host, hence it is the principle guiding the search for topological materials. Here we present a different type of topological matter, in which approximate symmetries stabilize near-degeneracies of bands. Specifically, we coin “quasi-symmetry” as a term for an exact symmetry of a Hamiltonian to lower-order yet is broken by higher-order perturbation terms. This enforces finite but parametrically small gaps at low-symmetry k-points across the whole Brillouin zone, eliminating the need for fine-tuning as the sources of large Berry curvature will occur at any arbitrary chemical potentials. |
Tuesday, March 7, 2023 8:36AM - 8:48AM |
F43.00002: 2D superconductivity in a nodal loop semimetal with purely 3D Fermi surfaces Qi Zhang, Shafayat Hossain, Zijia Cheng, Brian Casas, Zahir Muhammad, Weisheng ZHAO, Rajibul Islam, Carmine Autieri, Yu-Xiao Jiang, Maksim Litskevich, Tyler A Cochran, Luis Balicas, Zahid M Hasan The exotic properties of topological semimetals (TSMs) have attracted great attention and significant efforts have been made in exploring new topological phases and materials. Some of the TSMs are predicated to host exotic band properties, such as butterflylike coplanar ellipses nodal lines. Here in such a TSM, our transport experiments reveal a 2D superconductivity. This is very surprising given that our quantum oscillations experiments show 3D Fermi surface. We discuss the possible origin of the superconductivity in light of our angle-resolved photoemission spectroscopy and first-principles calculation results. |
Tuesday, March 7, 2023 8:48AM - 9:00AM |
F43.00003: Stacked Quantum Hall Effect in BaMnBi2 Subin Mali, Yingdong Guan, Lujin Min, Zhiqiang Mao, David E Graf Quantum Hall effect (QHE) in three dimensional materials have recently attracted intense interest. In this presentation, we report a stacked QHE in the layered Dirac material BaMnBi2. This compound possesses a non-centrosymmetric orthorhombic structure (Imm2) with alternating stack of 2D Bi zig-zag chain layers and Ba-MnBi4-Ba insulating slabs [1]. The non-centrosymmetric orthorhombic structure and strong spin-orbit coupling give rise to quasi-2D massive Dirac fermions with spin-valley locking. Recently, the bulk QHE has been experimentally verified in BaMnSb2 to come from spin-valley locked Dirac fermions [2]. Recent studies suggest that BaMnBi2 exhibits a spin-valley locked state differing from that in BaMnSb2 due to its weaker lattice distortion. Such a spin-valley locked state is also expected to yield a stacked QHE, but is not verified experimentally yet. From our magneto-transport measurements on BaMnBi2 bulk single crystals under high fields (up to 35T), we found evidence of stacked QHE. We observed not only two quantized Hall resistivity plateaus with filing factors of 1/2 and 3/2, but also the Zeeman splitting of the zeroth Landau level. These results deepen our understanding of the bulk spin-valley locked state in BaMnBi2. |
Tuesday, March 7, 2023 9:00AM - 9:12AM |
F43.00004: Quantum Hall and magneto-Seebeck effects in three-dimensional Dirac and Weyl semimetals Fenda R Pratama Large and non-saturating magneto-Seebeck coefficient Sxx as a function of magnetic field B is predicted [Sci. Adv. 4, eeat2621 (2018)] to occur in three-dimensional (3D) Dirac/Weyl semimetal (DWS). This is because by keeping the number of charge carriers n0 constant, the Hall resistivity is given by the classical formula ρyx=B/n0e (e is the elementary charge), while the thermoelectric Hall coefficient αxy approaches a finite value at the quantum limit (QL), where only the zeroth Landau level is occupied [PRB 99, 155123 (2019)]. Therefore, within the dissipationless limit, Sxx≈ρyx·αxy∝B. On the other hand, saturating Sxx is observed in 3D DWS ZrTe5, where 3D quantum Hall effect (QHE) occurs [Nat. Commun. 12, 3197 (2021)]. It was proposed [PRL 125, 206601 (2020)] that charge density wave (CDW) plays a decisive role in 3D QHE. However, transport measurement in ZrTe5 do not indicate the signs of CDW. |
Tuesday, March 7, 2023 9:12AM - 9:24AM |
F43.00005: Axial Gauge Fields in Laser Irradiated 3D Dirac Semimetals Hung-Hsuan Teh, Tokiro Numasawa, Takashi Oka Floquet engineering has become a powerful tool for understanding laser induced coherent phenomena in quantum materials[1]. It is noticed that an artificial axial gauge field (also known as chiral gauge field) can be realized[2] when emergent Floquet Weyl points appear in the Floquet spectrum[3]. Here, we concentrate on 3D Dirac semimetals irradiated by circularly polarized laser fields which lead to a Floquet Weyl pair. By utilzing the envelope profile of the laser field and considering the skin effect from the semimetal surface, nonzero axial electric and magnetic fields can be achieved. In this talk, we focus on physical consequences from the axial fields such as generation of currents and spectral features, and discuss their possible experimental signatures[4]. |
Tuesday, March 7, 2023 9:24AM - 9:36AM |
F43.00006: Automatic generation and topological classification of low-energy Hamiltonians at multi-fold degeneracies Kirill Alpin, Moritz M Hirschmann, Niclas Heinsdorf, Andreas Leonhardt, Wan Yee Yau, Xianxin Wu, Andreas P Schnyder In this talk, we show a method of generating general high-symmetry Hamiltonian with the goal of topologically classifying all possible multi-fold crossings in bandstructures of condensed matter systems. To do so, we found all higher-dimensional irreducible representations at all high-symmetry points in all space groups. The topological phase diagrams of the automatically generated low-energy Hamiltonian at these k-points were mapped out. During this process, we identified a prevalent topological phase with an unusually high Chern number of 5 in point crossings of space groups larger than 195. A material was found featuring this topological phase. Further ab-initio calculations of this materials surface density of states showed a high number of Fermi arcs. |
Tuesday, March 7, 2023 9:36AM - 9:48AM |
F43.00007: Weyl-Hubbard System: A Platform to Investigate the Interplay between Topology and Correlations Snehasish Nandy, Christopher A Lane, Jian-Xin Zhu The interplay between topology and electronic correlations may offer a rich avenue for discovering emergent quantum phenomena in condensed matter systems. In this work, starting from the Weyl-Hubbard system, we investigate the quantum Hall effect to explore the effect of onsite Hubbard correlations on nontrivial Weyl band topology in the presence of an external magnetic field. Within the Gutzwiller approximation, we find the system to undergo multiple topological phase transitions, including two Weyl phases with different pairs of Weyl nodes and a trivial narrow band insulator by tuning on-site Coulomb interaction and external magnetic field. Interestingly, these two Weyl phases can be distinguished by the sign of their chiral Landau levels. We also explore the possible experimental signature of these topological phases and correlation effects by calculating magnetic-field dependent Hall conductivity within the Kubo response theory. |
Tuesday, March 7, 2023 9:48AM - 10:00AM |
F43.00008: Topological responses to dislocations in inversion-breaking Weyl semimetals Lei Gioia Three-dimensional (3D) semimetals have established themselves to be a fruitful playground for novel topological physics. Recently it was discovered that 3D semimetals, with gaplessness protected via symmorphic symmetries, possess topological invariants associated with unquantized anomalies [1]. Such anomalies describe topological responses to lattice defects such as dislocations and disclinations. In this talk we will explore and extend these concepts in the context of both type-I and II Weyl semimetals with broken inversion symmetry. |
Tuesday, March 7, 2023 10:00AM - 10:12AM |
F43.00009: Massless Dirac fermions on a space-time lattice with a topologically protected Dirac cone Michal Pacholski, Alvaro Donis Vela, Gal Lemut, Jakub Tworzydlo, Carlo W Beenakker The symmetries that protect massless Dirac fermions from a gap opening may become ineffective if the Dirac equation is discretized in space and time, either because of scattering between multiple Dirac cones in the Brillouin zone (fermion doubling) or because of singularities at zone boundaries. Here we introduce an implementation of Dirac fermions on a space-time lattice that removes both obstructions. The quasi-energy band structure has a tangent dispersion with a single Dirac cone that cannot be gapped without breaking both time-reversal and chiral symmetries. We show that this topological protection is absent in the familiar single-cone discretization with a linear sawtooth dispersion, as a consequence of the fact that there the time-evolution operator is discontinuous at Brillouin zone boundaries. |
Tuesday, March 7, 2023 10:12AM - 10:24AM |
F43.00010: Weyl points in a quasicrystal stack and dense Fermi-Bragg arcs Andre G Fonseca, Thomas Christensen, John D Joannopoulos, Marin Soljacic We introduce a general mechanism for obtaining Weyl points in a stack of 2D quasicrystals, which can be extended to any stack of aperiodic layers. It relies on driving a topological phase transition by tuning the vertical crystal-momentum, forcing gap closures at the critical points. We illustrate our theory in a 3D generalization of the Qi-Wu-Zhang model defined on a Penrose quasicrystal. We establish the Weyl-point character of the band closings by a number of distinct signatures, including via the local Chern marker, the bulk dispersion, and the density of states. Interestingly, we also uncover an analogue of Fermi arcs in the quasicrystalline setting, manifested by densely distributed lines in the Fourier-resolved spectrum, in one-to-one correspondence with the Bragg peaks of the structure factor. Possible experimental realizations and connections to the recently observed band crossings in a stack of chalcogenide quasicrystals will also be discussed. |
Tuesday, March 7, 2023 10:24AM - 10:36AM |
F43.00011: Universal conductance fluctuations and crossover between symmetry classes in the Dirac semi-metal Cd3As2 Saurav Islam, Run Xiao, Yongxi Ou, Juan Chamorro, Tyrell M McQueen, Nitin Samarth Dirac semi-metals are a class of topological materials wherein both time-reversal symmetry and inversion symmetry co-exist. The application of a gate-voltage breaks inversion symmetry while magnetic field breaks time-reversal symmetry. This leads to changes in the symmetries of the ground state Hamiltonian, manifested through distinct signatures in universal conductance fluctuations which we probe here in nanowires of the prototypical Dirac semi-metal Cd3As2. We find a factor of √2 reduction in the magnitude of the universal conductance fluctuations as the magnetic field is increased, due to breaking time-reversal symmetry. In contrast, the magnitude of the fluctuations increases by a factor of 2√2 away from the charge neutrality point. Our experiments provide unequivocal evidence of universal conductance fluctuations as the source of intrinsic fluctuations in quantum transport measurements in mesoscopic Cd3As2 devices and establishes the usefulness of such measurements as a tool for probing topological phase transitions. |
Tuesday, March 7, 2023 10:36AM - 10:48AM |
F43.00012: Investigations of hybrid 2D semimetal heterostructures Eric K Lester, Chun-Chih Tseng, Elliott Runburg, Paul V Nguyen, Jarod Scribner, Paul T Malinowski, Xiaodong Xu, Jiun-Haw Chu, Matthew A Yankowitz, David H Cobden Besides graphene, the only well studied 2D semimetal is WTe2, which has strikingly different properties, including strong spin-orbit coupling, low symmetry, superconductivity and being a topological insulator in monolayers. We set out to investigate properties of hybrid combinations of these two semimetals, which could, for example, include strong induced spin-orbit coupling in the graphene or the modification of the superconductivity or excitonic pairing in the WTe2. We have studied a series of hybrid devices constructed with both monolayer and bilayer graphene and WTe2 and find charge transfer consistent with a work function difference. We analyze the effects on transport characteristics of upper and lower electrostatic gating, the application of magnetic fields, and we track the charge-neutral conditions for the constituent components and the sharing of charge between them. We identify emergent hybrid behavior that differs from that expected for a simple combination of the two materials in parallel. |
Tuesday, March 7, 2023 10:48AM - 11:00AM |
F43.00013: Novel 2D Dirac and Weyl Semimetals Guang Bian The discovery of graphene has stimulated enormous interest in two-dimensional (2D) electron gas with linear band structure. 2D Dirac materials possess many intriguing physical properties such as high carrier mobility and zero-energy Landau level for the relativistic dispersion and chiral spin/pseudospin texture. In this talk, we will discuss three new variants of 2D Dirac materials including (1) unpinned 2D Dirac semimetals in α-antimonene, (2) Rashba spin-split 2D Weyl semimetals, and (3) interacting Dirac states in graphene heterostructures. The results offer new insights into the relativistic behavior of electrons in reduced dimensions. |
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