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 P45: Topological Insulators Without Translation SymmetryLive
|
Hide Abstracts |
Sponsoring Units: DCMP Chair: Pallab Goswami, Northwestern University |
Wednesday, March 17, 2021 3:00PM - 3:12PM Live |
P45.00001: Rare region effects across a topological to trivial insulator quantum phase transition in three-dimensions Yixing Fu, Justin Wilson, Jed Pixley We revisit whether the disorder driven phase transition between trivial and topological insulators in three-dimensions remains a semimetal at weak disorder. While the (clean) Dirac semimetallic critical point is perturbatively stable, non-perturbative effects of rare regions have recently been shown to destabilize the semimetal phase by creating a finite density of states. This implies that an intervening diffusive metal phase may develop that has been overlooked in previous studies. We apply the kernel polynomial method to numerically calculate transport properties on large system sizes to determine the stability of this putative semimetal phase boundary. A qualitative picture of transport through tunneling between rare regions will be put forth. |
Wednesday, March 17, 2021 3:12PM - 3:24PM Live |
P45.00002: Skin effect and winding number in disordered non-Hermitian systems Jahan Claes, Taylor L Hughes Unlike their Hermitian counterparts, non-Hermitian (NH) systems may display an exponential sensitivity to boundary conditions and an extensive number of edge-localized states in systems with open boundaries, a phenomena dubbed the “non-Hermitian skin effect." The NH skin effect has recently been connected to the winding number, a topological invariant unique to NH systems. In this talk, I’ll present a real-space generalization of the winding number that applies to disordered systems. This real-space winding number is topological, in the sense that it remains quantized for a localized system, and this quantized value still predicts the NH skin effect. We use our theory to demonstrate the NH Anderson skin effect, in which a skin effect is developed as disorder is added to a clean system, as well as explain recent results in optical funnels. |
Wednesday, March 17, 2021 3:24PM - 3:36PM Live |
P45.00003: Multicriticality of Class D Disordered Topological Insulator in a Two-dimensional Lattice Model Tong Wang, Zhiming Pan, Ilya Gruzberg, Tomi Ohtsuki, Ryuichi Shindou A two-dimensional tight-binding model of a disordered topological insulator in class D is numerically studied by the transfer matrix method and the kernel polynomial expansion (KPE). We find a phase diagram exhibiting topological insulator (TI), diffusive metal (DM) and Anderson insulator (AI) phases. We clarify the critical behavior of the localization length, conductivity and density of states at a tricritical point [1-3], as well as the universality class of the DM-AI transition and TI-DM transitions. We compare our numerical results with a two-loop renormalization group study of 2D Dirac fermions with random mass [4]. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P45.00004: Topology of ordered and amorphous chiral matter Marcelo Guzmán, Denis Bartolo, David Carpentier Building on direct analogies with electronic matter, the concepts of topological insulator and topological protection have been successfully applied to a host of different physical systems as diverse as photonic metamaterials, geophysical fluids and mechanical structures. In this work we focus on materials having a chiral symmetry such as crystals with a sub-lattice symmetry and all mechanical systems assembled from beads and springs. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P45.00005: Structural and electronic properties of realistic two-dimensional amorphous topological insulators Bruno Focassio, Gabriel Ravanhani Schleder, Marcio Costa, ADALBERTO FAZZIO, Caio H Lewenkopf Using flat bismuthene as a platform, we systematically constructed realistic amorphous topological insulators systems through ab initio calculations. The radial distribution function shows that the obtained systems have short-range order and lack long-range order. We study the topological properties of these systems by calculating the topological invariants and characterizing the non-trivial topological band structure of our systems. The amorphization tends to suppress the bandgap but does not close it. We find that the survival of the QSH phase through the amorphization process is associated with the SOC strength of the material and the size of the bulk bandgap. Using full ab initio Hamiltonians, we investigate the Landauer conductance of systems with lengths up to 324 nm, comparable with experimental device sizes. We obtain that the topological helical edge states with quantized conductance are preserved inside the gap. For energies outside the topological gap region, we find a strong suppression of the conductance, consistent with Anderson localization. Furthermore, we show how to control the conductance by an exchange field induced by, for instance, suitable substrate proximity or an experimental probe. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P45.00006: Charge pumping in one dimensional quasicrystals characterized by Bott index Mao Yoshii, Sota Kitamura, Takahiro Morimoto In recent years, topological phases in quasiperiodic systems attract much attention. In these systems, we cannot use conventional methods defined in the momentum space for lack of periodicity. Hence, topological numbers in the quasiperiodic systems are calculated from the real space,. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P45.00007: Critical behavior of structurally disordered quantum Hall network models from an alternative scaling variable Elizabeth Dresselhaus, Bjoern Sbierski, Joel Ellis Moore, Ilya Gruzberg The nature of the quantum Hall plateau transition is a decades-old puzzle. The current consensus is that the Chalker Coddington network model captures the transition physics. Numerous works have used Lyapunov exponent finite-size scaling to calculate the localization length critical exponent ν ~ 2.6. However, calculations with the same methods on structurally disordered networks give a slightly different yet incompatible result, ν ~ 2.38, suggesting that structural disorder may be a relevant perturbation at the underlying fixed point. To further probe and understand this surprising finding, we study structurally disordered networks with an alternative scaling variable. This variable is based on the networks’ scattering matrices and does not require the quasi-1d geometry of conventional methods. We study networks an order of magnitude larger than the current literature standard to confirm the relevance of structural disorder and we also address the idea of marginal scaling at the critical point. Finally, we examine how these results are compatible with the Harris criterion. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P45.00008: Weak breaking of translational symmetry in Z2 Topological ordered states Peng Rao, Inti A Sodemann We study Z2 topologically ordered states enriched by translational symmetry by employing a recently developed 2D bosonization approach that implements an exact Z2 charge-flux attachement in the lattice. With this we develop a general description of a series of anomalous properties of these states, such as ground state degeneracy that depends on system size, the emergence of dangling Majorana modes and the 'weak symmetry breaking’ of translations. We demonstrate that this ‘weak symmetry breaking' of translations appears in certain states that are weak topological superconductors of the epsilon fermionic spinons, where they form stacks of Kitaev wires. This leads to the amusing property that there is no local operator that can translate the flux across a single Kitaev wire of fermonic spinons without paying an energy gap in spite of the vacuum remaining fully translational invariant. By extending the Z2 charge-flux attachment to open lattices and cylinders we construct a plethora of exactly solvable models providing an exact description of their dispersive Majorana gapless boundary modes. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P45.00009: Topological Hamiltonian and edge state detection using ARPES in amorphous systems1. Quentin Marsal, Daniel Varjas, Adolfo G Grushin
|
Wednesday, March 17, 2021 4:48PM - 5:00PM Live |
P45.00010: Quantum phase transition in the disordered topological insulator (Bi1-xSbx)2Se3 Karunya Shailesh Shirali, Duane D Johnson, Prashant Singh, William A Shelton, Ilya Vekhter First principles-based studies[1] have predicted that the disordered substitutional alloy (Bi1-xSbx)2Se3 undergoes a topological phase transition beyond a critical value of impurity concentration due to the decrease of the Spin-Orbit interaction. In their calculations, different methods yielded different values for the critical impurity concentration, which motivates us to perform systematic DFT-based simulations to study the topological phase transition. We perform simulations initially of x = 25, 50 and 75 percent Sb, including van der Waals interactions, with the goal of identifying the transition and analyzing the structural and electronic properties near the critical impurity concentration. To mimic substitutional disorder, we have constructed partially ordered supercells where the atomic pair correlations are zero up to the third nearest neighbor cell. |
Wednesday, March 17, 2021 5:00PM - 5:12PM Live |
P45.00011: Disordered topological crystalline insulators Raquel Queiroz, Zhida Song, Roni Ilan, Andrei B Bernevig, Ady Stern Topological phases are known for their robustness to local perturbations and for hosting extended states that evade the localization expected in low dimensional systems. Such states exist both on boundaries and in the bulk at the transitions between topological phases. This effect is epitomized in two-dimensions by the plateau transition of Chern bands dividing regions of different Chern numbers, either by varying energy or disorder strength. In the absence of a Chern invariant, crystalline symmetry may still protect the topology of two-dimensional systems. In this case, the topology may be fragile, which means that it is not robust to the mixing with trivial bands. In this talk, we explore the impact of disorder in two-dimensional topological systems protected by crystalline symmetry, the structure of their impurity states, and the possibility for the existence of delocalized states in the bulk. |
Wednesday, March 17, 2021 5:12PM - 5:24PM Live |
P45.00012: Revealing Dispersive Amorphous Electronic States on the Surface of a Glassy Topological Insulator Samuel Ciocys, Paul Corbae, Quentin Marsal, Daniel Varjas, Steven Eric Zeltmann, Adolfo G Grushin, Frances Hellman, Alessandra Lanzara The typical description of amorphous electronic structure assumes that a lack of translational symmetry ensures that momentum is ill-defined. This description is so pervasive in the amorphous field of study that the density of states is assumed to be momentum-independent, serving as the full characterization of an amorphous system's electronic structure. In this work, we uncover a highly dispersive, spin-momentum locked topological surface state in amorphous Bi2Se3 using Angle Resolved Photoemission Spectroscopy. We observe a Fermi surface with repeated annuli suggesting Bloch-like repetition and analogous Brillouin-like zones. We argue that amorphous structures conserve real-space length-scales, allowing for the existence of well-defined momentum-space length-scales, warranting a re-evaluation of amorphous band structure on the most fundamental level. |
Wednesday, March 17, 2021 5:24PM - 5:36PM Live |
P45.00013: Delocalization Transition of Disordered Axion Insulator Ady Stern, Zhida Song, Biao Lian, Raquel Queiroz, Roni Ilan, Andrei B Bernevig The axion insulator is a higher-order topological insulator protected by inversion symmetry. We show that under quenched disorder respecting inversion symmetry on average, the topology of the axion insulator stays robust, and an intermediate metallic phase in which states are delocalized is unavoidable at the transition from an axion insulator to a trivial insulator. We derive this conclusion from general arguments, from classical percolation theory, and from the numerical study of a 3D quantum network model simulating a disordered axion insulator through a layer construction. We find the localization length critical exponent near the delocalization transition to be ν=1.42±0.12. We further show that this delocalization transition is stable even to weak breaking of the average inversion symmetry, up to a critical strength. |
Wednesday, March 17, 2021 5:36PM - 5:48PM Live |
P45.00014: Disorder induced topology in quench dynamics Hsiu-Chuan Hsu, Pok Man Chiu, Po-Yao Chang We study the topology of quench dynamics in strongly-disordered one dimensional systems. We find the nontrivial topology of the post-quench state emerges above a finite disorder strength and survives in a certain range. This disorder-induced topological phase is confirmed by the entanglement-spectrum crossings and Berry phase flow. Furthermore, the dynamical Chern number is shown to be quantized with negligible small fluctuations. This disorder-induced topological phase in quench dynamics is reminiscent of the topological Anderson insulating phase in the equilibrium systems. Our work would inspire the investigation of the role of disorder in quench dynamics. |
Wednesday, March 17, 2021 5:48PM - 6:00PM Not Participating |
P45.00015: Topological properties of electronic states in quasiperiodic chains Shoichi Tsubota, Yutaka Akagi, Hosho Katsura In recent years, topological aspects of quasiperiodic systems have attracted much attention. However, due to the lack of translational symmetry, the conventional formulae for topological invariants are inapplicable to such systems and many of their topological properties remain unrevealed. In this study, we analyze topological properties of a tight-binding model on the Thue-Morse chain, which is one of the quasiperiodic chains. To diagnose the properties, we use local Berry phases, which are defined for individual bonds and quantized to 0 or π in the presence of symmetries such as spatial inversion. Physically, the π Berry phase corresponds to a local covalent bond and implies that topologically nontrivial edge states appear if the bond is broken. We verify that this is indeed the case for the bonds with inversion points. More remarkably, we find that some edge states appear to be nearly topological even if the broken bond is a bond without an inversion center, and the pattern of such bonds is quasiperiodic. These behaviors can be explained by the presence of partial inversion regions, where a part of atomic arrangements are inversion symmetric like palindromes. |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit 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 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700