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 X45: Topological Insulators: Theory IILive
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Sponsoring Units: DCMP Chair: Wladimir Benalcazar, Pennsylvania State University |
Friday, March 19, 2021 8:00AM - 8:12AM Live |
X45.00001: Magnetic impurities along the edge of a quantum spin-Hall insulator: realizing a one-dimensional AIII insulator Lars Fritz, Gerwin A.R. Van Dalum, Carmine Ortix In this paper we construct a one-dimensional insulator with an approximate chiral symmetry belonging to the AIII class and discuss its properties. The construction principle is the intentional pollution of the edge of a two-dimensional quantum spin-Hall insulator with magnetic impurities. The resulting bound states hybridize and disperse along the edge. We discuss under which circumstances this chain possesses zero-dimensional boundary modes on the level of an effective low-energy theory. The main appeal of our construction is the independence on details of the impurity lattice: the zero modes are stable against disorder and random lattice configurations. We also show that in the presence of Rashba coupling, which changes the symmetry class to A, one can still expect localized half-integer boundary excess charges protected by mirror symmetry although there is no non-trivial topological index. All of the results are confirmed numerically in a microscopic model. |
Friday, March 19, 2021 8:12AM - 8:24AM Live |
X45.00002: Effect of molecular-scale perturbations on Plasmons in Topological Insulators Yuling Guan, Zhihao Jiang, Stephan Wolfgang Haas We develop and apply a fully quantum mechanical approach to analyze the plasmonic excitation spectrum in the Su-Schrieffer-Heeger (SSH) model and its mirror symmetric(m-SSH) in the presence of molecule-scale perturbations. Strongly localized plasmons are observed in the host system due to the topological non-trivial single-particle edge states. Numerical evaluation of the RPA equations for the perturbed system show how the strength and position of the added impurities have strong effects on the degeneracy of localized collective excitations, i.e. the plasmonic energies shift and the spatial charge modulations change due to the perturbation. Furthermore, the plasmonic response to external electric fields is determined, which can be verified experimentally. |
Friday, March 19, 2021 8:24AM - 8:36AM Live |
X45.00003: Plasmons in Two-Dimensional Topological Insulators Henning Schloemer, Zhihao Jiang, Stephan Wolfgang Haas We analyze collective excitations in models of two-dimensional topological insulators, revealing characteristic signatures that distinguish different topological regimes by their plasmonic response. Using the random phase approximation in real and reciprocal space, we show how topology influences both bulk and surface plasmon properties. Bulk features are controlled by the overlap of the single particle wave functions, which in turn lead to a strong hardening and softening of inter- and intra-band plasmonic branches, respectively, in the topologically non-trivial regimes. Plasmonic surface modes are found to be governed by electronic transitions involving the mid-gap topological edge states, resulting in characteristic charge-density distributions localized at the boundaries of the system. |
Friday, March 19, 2021 8:36AM - 8:48AM Live |
X45.00004: Second-order topological insulator under strong magnetic field Benjamin Levitan, Tami Pereg-Barnea We study a three-dimensional chiral second-order topological insulator (SOTI) subject to a magnetic field. Via its gauge field, the applied magnetic field influences the electronic motion on the lattice, and via the Zeeman effect, the field influences the electronic spin. We compare an effective surface theory to a full lattice model of the SOTI. Without magnetic field, the surface theory shows good agreement with our lattice calculations, accurately predicting the surface gap as well as the spin and orbital components of the states at the edges of the surface Dirac bands. However, when a gauge field is applied, the Landau level spectrum obtained from the lattice theory deviates from that predicted by the surface theory. On any given surface, the lowest Landau level is found closer to zero energy than is predicted by the surface theory. Further, while the first excited levels approximately match their predicted spatial, spin, and (on-site) orbital dependence, these levels are missing their expected opposite-energy partners. |
Friday, March 19, 2021 8:48AM - 9:00AM Live |
X45.00005: Fragility of time-reversal symmetry protected topological phases Max McGinley, Nigel R Cooper Time-reversal symmetry (TRS) underpins many interesting phenomena in quantum mechanics, including certain topological phases such as topological insulators and the Haldane phase. However, even if present at the microscopic level, TRS is effectively broken in the dynamics of open systems. In this talk, I will argue that phenomena protected by TRS are fundamentally unstable against coupling to their surroundings. System-environment interactions lead to the breaking of TRS in the sense that the system propagates irreversibly, and this same mechanism gives rise to processes that would be forbidden by TRS in an isolated system, thus compromising TRS-protected phenomena. Specifically, I will demonstrate that topological bound states at the edges of 1D topological systems protected by TRS are inevitably subject to decoherence. Analogously, in 2D systems this same mechanism compromises the quantized conductance of helical edge modes. Our results elucidate potential challenges in utilizing topological systems for quantum technologies, and may account for resistance measurements seen in experiments on quantum spin Hall systems. |
Friday, March 19, 2021 9:00AM - 9:12AM Live |
X45.00006: 3d topological insulator in Weyl semimetal in the presence of commensurate magnetic field Md. Faruk Abdulla, Ankur Das, Sumathi Rao, Ganpathy N Murthy We study the effect of commensurate magnetic field in a time reversal broken 3d Weyl semimetal [1]. The mass term (M) which dictates the location of Weyl nodes at zero field, causes a transition from trivial insulator to Weyl-semimetal(at M = Mc1 ) to topological insulator (at M=Mc2 ) in the presence commensurate magnetic field. There are 2q number of Weyl nodes for Mc1 < M < Mc2 . For M > Mc2 , we get the signature of three-dimensional topological insulator with arc like gapless surface states with length 2π. Mc1 and Mc2 change as we change q such that (Mc1−Mc2 ) goes to zero exponentially with increasing q. |
Friday, March 19, 2021 9:12AM - 9:24AM Live |
X45.00007: Open quantum dot model based on 3D topological insulator nanowire Ruchi Saxena, Eytan Grosfeld, Sebastian de Graaf, Tobias Lindstrom, Floriana Lombardi, Eran Ginossar The visibility of the protected surface states of a three-dimensional topological insulator (TI) in transport experiments is strongly suppressed due to the residual bulk contribution to electronic transport. However, TI nanoribbons (TINR) have proven very effective in enhancing the surface state contribution as has been experimentally evidenced by Aharonov-Bohm oscillations. We propose a TINR geometry which can potentially confine the surface electronic states also in the second direction, along the TINR. In this geometry, in the sub-gap region, we find resonant transmission due to the formation of bound states at certain energies. We theoretically study the resonant electron tunnelling through such a quantum dot (QD) attached to TINR leads as a function of the system parameters within the Landauer-Buttiker formalism. We also investigate the smooth and sharp interfaces incorporating the effect of spin-connection which plays an important role in the motion of the Dirac particles in curved space. Further, we analyse the effect of Coulomb blockade on the properties of the TI QD and discuss relevant system parameters that are useful to experimentally realize a QD based on the TINR. |
Friday, March 19, 2021 9:24AM - 9:36AM Live |
X45.00008: Toward Exact Bulk-boundary Correspondence for Zero-energy Corner States Minwoo Jung, Yang Yu, Gennady Shvets We refine some of weakly established bulk-boundary correspondence regarding zero-energy corner states (ZCS) in two-dimensional (2D) crystalline insulators, and reveal that bulk polarization fails to be a relevant indicator of ZCSs. Our analysis using multilayer stacking construction of C^3-symmetric crystalline insulators demonstrates that ZCSs in breathing Kagome lattices are attributed to Z_2 Zak phase of their edge band and that Z_3 bulk polarization is not correlated well with the existence of ZCSs. Also, we show that the ZCSs in C^4-symmetric crystalline insulators are a result of chiral symmetry and topological half charge at half-filling, and that the bulk polarization at quarter-filling fails to explain the emergence of a ZCS. Lastly, we provide a 2D Hamiltonian model supporting a ZCS despite completely trivial topology both in its bulk and edge. Our work, therefore, elucidates that overlapping phase diagrams of a bulk invariant and a boundary signature don't necessarily guarantee a solid bulk-boundary correspondence. |
Friday, March 19, 2021 9:36AM - 9:48AM Live |
X45.00009: Dynamic impurities in two-dimensional topological insulator edge states Simon Wozny, Martin Leijnse, Sigurdur I. Erlingsson Two-dimensional topological insulators host one-dimensional helical states at the edges. |
Friday, March 19, 2021 9:48AM - 10:00AM Live |
X45.00010: Mapping rules from nodal line semimetal to topological crystalline insulator in face centered cubic lattice Ikuma Tateishi We study what kind of topological crystalline insulator phase emerges from nodal line semimetal phases in the face centered cubic system, which is not indicated by topological indices when spin-orbit coupling (SOC) is introduced. We construct an effective model, which hosts two different nodal lines phases, and calculated mirror Chern numbers in it by introducing SOC. As a result, we find that the two nodal line phases with different nodal line configurations are mapped to different topological crystalline insulator phases. This result shows that turning off SOC and checking the nodal line configuration can distinguish the two topological crystalline insulator phases, which have not been distinguished by previous methods. |
Friday, March 19, 2021 10:00AM - 10:12AM Live |
X45.00011: The Landau levels of Euler insulator Yifei Guan, Oleg Yazyev, Adrien Bouhon A fragile topology in 2-band subspaces protected by either PT or C2T symmetries in 2D is characterized by a Z Euler class, which would degenerate to a Z2 second Stiefel-Whitney class if the bands are connected to extra bands. We investigate the energy levels of such Euler fragile topological materials in the presence of an external magnetic field. As a consequence of the topology, a gap closing in the Hofstadter spectrum occurs at nonzero Euler class. Furthermore, larger Euler numbers lead to gap closing at smaller flux, even if the total Hall conductance is always zero. We propose an interpretation of the Landau level behaviour under the framework of Chern basis. |
Friday, March 19, 2021 10:12AM - 10:24AM Live |
X45.00012: Universal Approach to Magnetic Second-Order Topological Insulator Cong Chen We propose a universal practical approach to realize magnetic second-order topological insulator (SOTI) materials, based on properly breaking the time reversal symmetry in conventional (first-order) topological insulators. The approach works for both three dimensions (3D) and two dimensions (2D) and is particularly suitable for 2D, where it can be achieved by coupling a quantum spin Hall insulator with a magnetic substrate. Using first-principles calculations, we predict bismuthene on EuO(111) surface as the first realistic system for a two-dimensional magnetic SOTI. We explicitly demonstrate the existence of the protected corner states. Benefitting from the large spin-orbit coupling and sizable magnetic proximity effect, these corner states are located in a boundary gap ∼83 meV, and hence can be readily probed in experiment. By controlling the magnetic phase transition, a topological phase transition between a first-order TI and a SOTI can be simultaneously achieved in the system. The effect of symmetry breaking, the connection with filling anomaly, and the experimental detection are discussed. |
Friday, March 19, 2021 10:24AM - 10:36AM Live |
X45.00013: magnetic field driven 2D spin-orbit coupled system Yiheng Xu, Congjun Wu We consider a two-dimensional spin-orbit coupled system subjected to an in-plane magnetic field, which can be realized in the Rashba spin-orbit coupled system or the surface state of a topological insulator. Although the static Zeeman magnetic field does not induce an electric current, a time-dependent one can induce such a current in the direction perpendicular to the Zeeman field. Since the spin-orbit coupling can be viewed as a consequence of an electric field perpendicular to the 2D plane, the electric field, the magnetic field, and the response current form a triad, which is different from the Hall effect in which the magnetic field is out of plane while the electric field is in plane. |
Friday, March 19, 2021 10:36AM - 10:48AM Live |
X45.00014: Two-loop renormalization group analysis of 2D Dirac fermion with random mass Zhiming Pan, Tong Wang, Tomi Ohtsuki, Ilya Gruzberg, Ryuichi Shindou We perform a two-loop renormalization group analysis for Dirac fermions with random mass in 2-epsilon dimensions. In two dimensions, the random mass is marginally irrelevant at the clean-limit fixed point, but in the two-loop analysis we find an IR unstable fixed point at a finite disorder strength. Using the epsilon expansion [1,2,3], we evaluate the localization length exponent, the dynamical exponent, and the scaling dimension of the (uniform) mass term at the IR unstable fixed point. We compare our results with earlier 3-loop [4] and 4-loop [5] calculations for the massless Gross-Neveu model. |
Friday, March 19, 2021 10:48AM - 11:00AM Live |
X45.00015: Many-Body Invariants for Chern and Chiral Hinge Insulators Byungmin Kang, Wonjun Lee, Gil Young Cho We construct new many-body invariants for 2d Chern and 3d chiral hinge insulators characterizing quantized pumping of bulk dipole and quadrupole moments. The many-body invariants are written entirely in terms of many-body ground state wavefunctions on a torus geometry with twisted boundary conditions and a set of unitary operators. We present a number of supporting evidences for the invariants via topological field theory interpretation, adiabatic pumping argument, and direct mapping to free-fermion band indices. Therefore, the invariants explicitly encircle several different pillars of theoretical descriptions of topological phases. Furthermore, our many-body invariants are written in forms which can directly be employed in various numerics including the exact diagonalization and the density-matrix renormalization group simulations. We finally confirm our invariants by numerical computations including infinite density matrix renormalization group on quasi-one-dimensional systems. |
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