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 T25: Theory of Topological Insulators and Topological Band Structures |
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Sponsoring Units: DCMP Chair: Kai-Jie Yang, Pennsylvania State University Room: Room 217/218 |
Thursday, March 9, 2023 11:30AM - 11:42AM |
T25.00001: Topologically localized insulators Bastien Lapierre, Titus Neupert, Luka Trifunovic Topological insulators are known for obstructing Anderson localization. In this talk, I will introduce a three-dimensional insulating topological phase, dubbed "Topologically Localized Insulator" (TLI), whose existence is enabled by the phenomenon of Anderson localization. Interestingly, although the bulk of TLI is fully localized, it has isotropic and quantized magnetoelectric polarizability tensor while its boundary has quantized Hall conductance. |
Thursday, March 9, 2023 11:42AM - 11:54AM |
T25.00002: Theory of oblique topological insulators Benjamin T Moy, Hart Goldman, Ramanjit Sohal, Eduardo H Fradkin A long-standing problem in the study of topological phases of matter has been to understand the types of fractional topological insulator (FTI) phases possible in 3+1 dimensions. Unlike ordinary topological insulators of free fermions, FTI phases are characterized by fractional Θ-angles, long-range entanglement, and fractionalization. Starting from a simple family of ZN lattice gauge theories due to Cardy and Rabinovici, we develop a class of FTI phases based on the physical mechanism of oblique confinement and the modern language of generalized global symmetries. We dub these phases oblique topological insulators. Oblique TIs arise when dyons—bound states of electric charges and monopoles—condense, leading to FTI phases characterized by topological order, emergent one-form symmetries, and gapped boundary states not realizable in 2+1-D alone. Based on the lattice gauge theory, we present continuum topological quantum field theories (TQFTs) for oblique TI phases involving fluctuating one-form and two-form gauge fields. We demonstrate that these theories exhibit a universal "generalized magnetoelectric effect'' in the presence of two-form background gauge fields. Moreover, we characterize the possible boundary topological orders of oblique TIs, finding a new set of boundary states not studied previously for these kinds of TQFTs. |
Thursday, March 9, 2023 11:54AM - 12:06PM |
T25.00003: Emergent Quantum Fractality on the Surface of Topological Insulators Lakshmi Pullasseri Madom Narayana Iyer, Daniel Shaffer, Luiz H Santos
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Thursday, March 9, 2023 12:06PM - 12:18PM |
T25.00004: New characterization of non-Hermitian skin effects Yusuke Nakai, Nobuyuki Okuma, Masatoshi Sato Recently, non-Hermitian systems, whose dynamics are effectively described by non-Hermitian Hamiltonians, have been extensively studied. The non-Hermitian skin effects are boundary phenomena intrinsic to non-Hermitian systems, where the energy spectra under the open boundary condition (OBC) drastically differ from those under the periodic boundary condition (PBC). In this presentation, we discuss the new characterization of non-Hermitian skin effects. We find that this characterization well-describes phase transitions of non-Hermitian skin effects with and without symmetry. |
Thursday, March 9, 2023 12:18PM - 12:30PM |
T25.00005: Geometric Origin of Non-Bloch PT Symmetry Breaking Yu-Min Hu, Hong-Yi Wang, Zhong Wang, Fei Song The parity-time (PT) symmetry of a non-Hermitian Hamiltonian leads to real (complex) energy spectrum when the non-Hermiticity is below (above) a threshold. Recently, it has been demonstrated that the non-Hermitian skin effect generates a new type of PT symmetry, dubbed the non-Bloch PT symmetry, featuring unique properties such as high sensitivity to the boundary condition. Despite its relevance to a wide range of non-Hermitian lattice systems, a general theory is still lacking for this generic phenomenon even in one spatial dimension. Here, we uncover the geometric mechanism of non-Bloch PT symmetry and its breaking. We find that non-Bloch PT symmetry breaking occurs by the formation of cusps in the generalized Brillouin zone (GBZ). Based on this geometric understanding, we propose an exact formula that efficiently determines the breaking threshold. Finally, we predict a new type of spectral singularities associated with the symmetry breaking, dubbed non-Bloch van Hove singularities, whose physical mechanism fundamentally differs from their Hermitian counterparts. |
Thursday, March 9, 2023 12:30PM - 12:42PM |
T25.00006: Correlation effects on non-Hermitian topological classifications Tsuneya Yoshida, Yasuhiro Hatsugai Extensive studies in these years have discovered a variety of exotic phenomena for non-Hermitian systems[1-4] such as the emergence of exceptional points[5] and skin effects[6]. So far, most of the works have focused on non-interacting systems. However, recent the development of technology allows to fabricate non-Hermitian correlated systems for cold atoms[7], which poses the following question: correlation effects on non-Hermitian topology. |
Thursday, March 9, 2023 12:42PM - 12:54PM Author not Attending |
T25.00007: Transport Signatures of Amorphous 3D Topological Insulator Siddhant Mal, Elizabeth Dresselhaus, Joel E Moore
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Thursday, March 9, 2023 12:54PM - 1:06PM |
T25.00008: Quantum theory of nonlinear magnetotransport in topological insulators Mandela Mehraeen, Shulei Zhang Increasing attention has been paid to nonlinear magnetotransport effects in topological insulators, which may be used as a powerful tool to probe the topological surface states and spin-orbit interaction. In this work, we theoretically investigate the nonlinear charge transport in a three-dimensional topological insulator by using a formal quantum approach. We find that both a longitudinal and a transverse nonlinear resistance may emanate from the interplay of the topological surface state with spin-momentum locking and random interfacial disorder. Interestingly, these nonlinear magnetoresistances can be significantly enhanced as the carrier density is reduced. And both of them exhibit unusual dependencies on the magnetic field, which make them differentiable from those that rely on hexagonal warping or current-induced spin polarization. |
Thursday, March 9, 2023 1:06PM - 1:18PM |
T25.00009: Geometric contribution to the longitudinal conductivity in insulators Ilia Komissarov, Tobias Holder, Raquel Queiroz In recent years, quantum geometry of the Hilbert space became a unified language to describe various optical and condensed matter phenomena. However, compared to the better-known Berry curvature, we hear less about the quantum (Fubini-Study) metric gαβ as it is hard to observe directly. gαβ is nevertheless of the utmost importance as it parameterizes the quantum distance between states in the Hilbert space and can be related to the spread of the wavefunctions, which is of interest for unconventional superconductivity and Quantum Hall physics. |
Thursday, March 9, 2023 1:18PM - 1:30PM |
T25.00010: Topological gap labeling with third Chern numbers in three-dimensional quasicrystals Kazuki Yamamoto, Mikito Koshino We study the topological gap labeling of general three-dimensional quasicrystals and we find that every gap in the spectrum is characterized by a set of third Chern numbers. |
Thursday, March 9, 2023 1:30PM - 1:42PM |
T25.00011: Coupling Lattice Curvature and Electromagnetism in Topological Insulators Julian May-Mann, Mark R Hirsbrunner, Xuchen Cao, Taylor L Hughes Quantized responses are important tools for understanding and characterizing the universal features of topological phases of matter. Here, we consider a class of topological insulators in 3D with n-fold lattice rotation symmetry. These insulators realize quantized mixed geometry-charge responses, where line-like disclination defects of the lattice carry fractionally quantized electric polarization. When the surface of these insulators is gapped, disclinations of the surface carry a fractional charge that is half the minimal amount that can occur in purely 2D systems. These effects and other related phenomena, are captured by a 3D topological response term that couples the lattice curvature to the electromagnetic field strength. In this talk, we will discuss the origin and physical observables of this topological response term, and how it can be realized in real lattice systems. |
Thursday, March 9, 2023 1:42PM - 1:54PM |
T25.00012: Bulk-boundary correspondence in point-gap topological phases Daichi Nakamura, Takumi Bessho, Masatoshi Sato The bulk-boundary correspondence (BBC) is a fundamental principle in Hermitian topological phases. It, however, has been known that the BBC may break down in non-Hermitian systems. The key is the difference between the bulk spectra under open boundary conditions (OBCs) and that under periodic boundary conditions (PBCs) due to the non-Hermitian skin effect. Since non-Hermitian Hamiltonians take the complex energy, we can define two types of topological phases, line-gap and point-gap topological phases. Many previous works have shown that the BBC becomes valid again for the line-gap topological phases if the bulk spectra under OBCs are treated properly. On the other hand, the BBC for the point-gap topological phases has remained unclear. Here, we clarify that the classification of bulk point-gap topological phases in OBCs can be different from those in PBCs. Moreover, we show that the BBC also exists for the point-gap topological phases by introducing real-space point-gap topological numbers defined under OBCs. |
Thursday, March 9, 2023 1:54PM - 2:06PM |
T25.00013: Spin texture of fragile topology Gunnar F Lange, Adrien Bouhon, Robert-Jan Slager Topological phases are have been the subject of intense studies over the recent years, as they are interesting both from a fundamental theoretical |
Thursday, March 9, 2023 2:06PM - 2:18PM |
T25.00014: Non-Abelian multi-gap topology of materials Adrien Bouhon, Robert-Jan Slager, Tomas Bzdusek We address the quantization of non-Abelian multi-gap topological charges in crystalline materials’ band structures. Recent experimental and theoretical advances have addressed these uncharted multi-gap topological phases that arise upon braiding nodal points formed by successive energy bands, which can in turn be quantified by 2D invariants such as Euler class. We here address subtleties of this physics in intrinsic 1 spatial dimension and in 1D Brillouin paths of higher dimensional lattices and show that a priori the non-Abelian multi-gap charges are not quantized. Rather, we find that only under strict conditions one retrieves meaningful 1D quantization, therefore putting a subset of recent results and claims in a critical context and providing for the necessary conditions to have 1D multi-gap topology. Our results finally pave the way to define generic models in both intrinsic 1D and sub-dimensional contexts that can aid pursuits in (meta-) material realizations. The outlook will be the systematic cataloging of the non-Abelian multi-gap topology of crystalline materials. |
Thursday, March 9, 2023 2:18PM - 2:30PM |
T25.00015: Theory of Glide Symmetry Protected Helical Edge States in WTe2 Monolayer Maciej Bieniek, Jukka Vayrynen, Gang Li, Titus Neupert, Ronny Thomale We theoretically investigate electronic and transport properties of QSH edge states in large gap 1-T' WTe2 monolayers. We explore the impact of edge termination, disorder, temperature, and interactions on experimentally addressable edge state observables, such as local density of states and conductance. We show that conductance quantization can remain surprisingly robust even for heavily disordered samples because of an anomalously small edge state decay length and additional protection related to the large direct gap allowed by glide symmetry. From the simulation of temperature-dependent resistance, we find that moderate disorder enhances the stability of conductance by localizing bulk states. We evaluate the edge state velocity and Luttinger liquid parameter as functions of the chemical potential, finding prospects for physics beyond linear helical Luttinger liquids in samples with ultra-clean and well-defined edges. |
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