Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R54: Topological Phase Transitions |
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Sponsoring Units: DCMP Chair: Kamal Choudhary Room: Mile High Ballroom 2A |
Thursday, March 5, 2020 8:00AM - 8:12AM |
R54.00001: Self-duality of the integer quantum Hall to insulator transition: a composite fermion description Prashant Kumar, Kevin S Huang, Yong-Baek Kim, Srinivas Raghu The integer quantum Hall to insulator transition (IQHIT) is a paradigmatic quantum critical point. Key aspects of this transition, however, remain mysterious, due to the simultaneous effects of quenched disorder and strong interactions. We study this transition using a composite fermion (CF) representation, which incorporates some of the effects of interactions. As we describe, the transition also marks a IQHIT of CFs: this suggests that the transition may exhibit self-duality. We show the explicit equivalence of the electron and CF Lagrangians at the critical point via the corresponding non-linear sigma models, revealing the self-dual nature of the transition. We show analytically that the resistivity tensor at the critical point is ρ_{xx} = ρ_{xy} = e^{2}/h, which are consistent with the expectations of self-duality, and in rough agreement with experiments. |
Thursday, March 5, 2020 8:12AM - 8:24AM |
R54.00002: Superuniversality of topological quantum phase transitions Alexander Tyner, Pallab Goswami Since two topologically distinct phases cannot be adiabatically deformed into each other, they must be separated by a sharp phase transition. Therefore, our understanding of global phase diagrams of topological quantum materials remains incomplete without addressing the nature of topological quantum critical points. We will show that irrespective of underlying symmetry classes, the universal behaviors of several topological phase transitions at different spatial dimensions are controlled by massless Dirac fermion fixed points. Based on this idea of superuniversality, we will address the scaling properties of topological quantum critical points for different Altland-Zirnbauer symmetry classes. |
Thursday, March 5, 2020 8:24AM - 8:36AM |
R54.00003: Identification of Topological Phase Transitions in Kitaev Quantum Spin Liquids Ara Go, Kyusung Hwang, Beom Hyun Kim, Ji Heon Seong, Eun-Gook Moon We investigate physical quantities of a spin model and argue that magnetic field angle dependence and resonant inelastic X-ray scattering may probe topological phase transitions in Kitaev quantum spin liquids (KQSLs). By using exact-diagonalization, spin-wave theory, and parton mean field analysis, characteristic signatures of topological phase transitions in KQSLs are obtained in a spin model with the Kitaev, Heisenberg, and off-diagonal symmetric terms. Especially, we find qualitative differences between KQSLs and zig-zag ordered phases. We also apply our results to a candidate system α-RuCl3 and provide smoking-gun experiments. |
Thursday, March 5, 2020 8:36AM - 8:48AM |
R54.00004: Probing Topological Phase Transition Using Rotational Second-Harmonic Generation in (Bi_{1-x}Sb_{x})_{2}Se_{3} Kun Zhao, Silu Huang, Jisun Kim, Matthew T Curtis, Joel E Taylor, Louis H Haber, Rongying Jin, E Ward Plummer Topological phase transitions have attracted significant attention recently. (Bi_{1-x}Sb_{x})_{2}Se_{3} demonstrates a metal-insulator transition as well as a topological phase transition from a topological insulator to a normal insulator driven by isoelectronic substitution. Although this topological phase transition has been studied both theoretically and experimentally for thin films and single crystals, very conflicting results have been reported and the critical transition point is still under debate. The symmetric study of surface electronic symmetry has never been conducted. Rotational second-harmonic generation (RSHG) is a powerful and non-invasive nonlinear optical technique for probing the electronic symmetry originating from broken symmetry at the surface. In this talk, we symmetrically characterize the surface electronic symmetry and the topological phase transition using high-quality (Bi_{1-x}Sb_{x})_{2}Se_{3} single crystals. From the RSHG patterns, we confirm the Bi_{2}Se_{3} surface shows a C_{3v} symmetry and the Sb_{2}Se_{3} surface shows a C_{2v} symmetry. By analyzing the evolution of RSHG patterns with substitution concentration, the critical transition point is further derived. The interplay between the topological phase transition and the metal-insulator transition is also discussed. |
Thursday, March 5, 2020 8:48AM - 9:00AM |
R54.00005: Topological Phase Transitions in a Hybridized Three-Dimensional Topological Insulator Su Kong Chong, Lizhe Liu, Feng Liu, Taylor D. Sparks, Vikram V. Deshpande As the three-dimensional (3D) topological insulator (TI) approaches its 2D thickness limit, quantum tunneling between top and bottom surfaces turns their gapless Dirac band into a gapped state at the Dirac points. Analytical formulation suggests that the hybridization gap scales exponentially with a decrease in number of layers while the system oscillates between topologically trivial and non-trivial insulators. This work explores the transport properties of a 3D TI in the inter-surface hybridization regime. By experimentally probing the hybridization gap as a function of TI thickness using three different methods, namely thermal activation, differential conductance, and quantum capacitance, we map the crossover from 3D TI to 2D insulating state. We detect gap-closing features in the moderate hybridization regime with a perpendicular electric field, suggesting topological phase transitions in the regime. In certain parameter spaces of the non-trivial insulator, we observe quantization of the longitudinal conductance at 2e^{2}/h indicating the quantum spin Hall state. |
Thursday, March 5, 2020 9:00AM - 9:12AM |
R54.00006: Quasi-periodic dynamical phase transitions in multi-band topological insulators Nicholas Sedlmayr Dynamical phase transitions are non-equilibrium phenomena where non-analyticities occur in dynamically evolving correlation functions, in analogy with the non-analyticities in the derivatives of the free energy for a standard phase transition. Topological phase transitions sperate phases of equivalent symmetry but different topology. The ways in which these two phenomena can be connected has recently become a topic of great interest. Here we will report on dynamical phase transitons in many-band one dimensional topological insulators which demonstrate curious quasi-periodic, rather than periodic, dynamical phase transitions. Furthermore we will consider the role of the topologically protected edge states in the dynamics and connections with fidelity susceptibility and dynamical entanglement entropy. |
Thursday, March 5, 2020 9:12AM - 9:24AM |
R54.00007: Topological multicriticality of spin-orbit coupled electrons in one dimension Mariana Malard, David Brandao, Paulo E. de Brito, Henrik Johannesson A central tenet in the theory of quantum phase transitions (QPTs) is that a nonanalyticity in the ground state energy in the thermodynamic limit implies a QPT. Here we report on a finding that challenges this assertion. As a case study we take the phase diagram of a one-dimensional band insulator with spin-orbit coupled electrons with trivial and topological gapped phases separated by intersecting critical surfaces. The intersections define multicritical lines across which the ground state energy becomes nonanalytical, but with no phase transition taking place. We propose a simple picture for how multicriticality gives rise to this unexpected phenomenon. |
Thursday, March 5, 2020 9:24AM - 9:36AM |
R54.00008: Construction of second-order topological phases protected by chiral symmetry Ryo Okugawa, Shin Hayashi, Takeshi Nakanishi We investigate topological phase transitions of a model to construct two-dimensional second-order topological insulators protected by chiral symmetry. By the theory of the topological phase transitions, we propose second-order topological semimetallic and insulating phases with flat hinge bands in chiral-symmetric three-dimensional systems. We also demonstrate the various second-order topological phases by constructing a two-dimensional lattice model from the Su-Schrieffer-Heeger models and by stacking the lattice models. |
Thursday, March 5, 2020 9:36AM - 9:48AM |
R54.00009: Piezoelectricity and Topological Quantum Phase Transitions in Two-Dimensional Spin-Orbit Coupled Crystals with Time-Reversal Symmetry Jiabin Yu, Chao-Xing Liu Topological quantum phase transitions can be reflected by the sudden jump of certain physical response functions, e.g., the transition between quantum spin Hall state and normal insulator state featured by the jump of the two-terminal conductance. In this work, we demonstrate that the piezoelectric response can also change discontinuously across a topological quantum phase transition in two-dimensional time-reversal invariant systems with spin-orbit coupling. We study all gap closing cases for all 7 plane groups that allow non-vanishing piezoelectric tensor and find that any gap closing with 1 fine-tuning parameter between two gapped states changes either the Z2 invariant (characterizing the quantum spin Hall phase) or the "locally" stable valley Chern number (characterizing the valley Hall phase). The jump of the piezoelectric response is found to exist for all these transitions, and we propose the HgTe/CdTe quantum well and BaMnSb2 as two potential experimental platforms. |
Thursday, March 5, 2020 9:48AM - 10:00AM |
R54.00010: Vortex and Surface Phase Transitions in Superconducting Higher-order Topological Insulators Sayed Ali Akbar Ghorashi, Taylor L Hughes, Enrico Rossi Topological insulators (TIs) having intrinsic or proximity-coupled s-wave superconductivity host Majorana zero modes (MZMs) at the ends of vortex lines. The MZMs survive up to a critical doping of the TI at which there is a vortex phase transition that eliminates the MZMs. In this work, we show that the phenomenology in higher-order topological insulators (HOTIs) can be qualitatively distinct. In particular, we find two distinct features.(i) We find that vortices placed on the gapped (side) surfaces of the HOTI, exhibit a pair of phase transitions as a function of doping. The first transition is a surface phase transition after which MZMs appear. The second transition is the well-known vortex phase transition. We find that the surface transition appears because of the competition between the superconducting gap and the local T-breaking gap on the surface.(ii) We present numerical evidence that shows strong variation of the critical doping for the vortex phase transition as the center of the vortex is moved toward or away from the hinges of the sample. We believe our work provides new phenomenology that can help identify HOTIs, as well as illustrating a promising platform for the realization of MZMs. |
Thursday, March 5, 2020 10:00AM - 10:12AM |
R54.00011: Topological invariants and edge modes at quantum criticality Ruben Verresen, Ryan Thorngren, Nick G. Jones, Frank Pollmann, Ashvin Vishwanath It is sometimes presumed that a finite correlation length is essential to stabilizing topological phenomena. This applies even to well-studied topological semi-metals, where one appeals to gapped degrees of freedom (in momentum-space). In this talk, I will show that this common wisdom is not justified: topological invariants and edge modes can survive at phase transitions. This leads to the novel notion of symmetry-enriched quantum criticality, examples of which are hiding in plain sight. |
Thursday, March 5, 2020 10:12AM - 10:24AM |
R54.00012: Landau-forbidden quantum phase transitions between bosonic Z2 symmetry-protected topological phases in 2+1D Maxime Dupont, Snir Gazit, Thomas Scaffidi We perform a Quantum Monte Carlo study of quantum phase transitions between different classes of Z2 bosonic symmetry-protected topological (SPT) phases in 2+1D. This is made possible by an advantageous choice of basis which takes care of the sign problem that one might naively expect. Depending on the classes of SPTs considered, we find a variety of unusual intermediate symmetry-broken phases, as well as evidence for a quantum critical direct transition. |
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