Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session K03: Quantum Effects in Topological SystemsFocus

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Sponsoring Units: DCMP Chair: Andrew Rasmussen, Northwestern Univ Room: BCEC 107B 
Wednesday, March 6, 2019 8:00AM  8:12AM 
K03.00001: Classification and construction of higherorder symmetry protected topological phases of interacting bosons Alexander Rasmussen, Yuanming Lu Motivated by the recent discovery of higherorder topological insulators, we study their counterparts in strongly interacting bosons: `higherorder symmetry protected topological (HOSPT) phases'. While the usual (1storder) SPT phases in d spatial dimensions support anomalous (d1)dimensional surface states, HOSPT phases in d dimensions are characterized by topological boundary states of dimension (d2) or smaller, protected by certain global symmetries and robust against disorders. Based on a dimensional reduction analysis, we show that HOSPT phases can be built from lowerdimensional SPT phases in a way that preserves the associated crystalline symmetries. When the total symmetry is a direct product of global and crystalline symmetry groups, we are able to classify the HOSPT phases using the Künneth formula of group cohomology. Based on a decorated domain wall picture of the Künneth formula, we show how to systematically construct the HOSPT phases, and demonstrate our construction with many examples in two and three dimensions. 
Wednesday, March 6, 2019 8:12AM  8:24AM 
K03.00002: Intrinsically interacting topological crystalline insulators and superconductor Alexander Rasmussen, Yuanming Lu Motivated by recent progress in crystalline symmetry protected topological (SPT) phases of interacting bosons, we study topological crystalline insulators/superconductors (TCIs) of strongly interacting fermions. We construct a class of intrinsically interacting fermionic TCIs, and show that they are beyond both freefermion TCIs and bosonic crystalline SPT phases. We also show how these phases can be characterized by symmetry protected gapless corner/hinge states. 
Wednesday, March 6, 2019 8:24AM  8:36AM 
K03.00003: Disorderinduced helical phase in magnetic topological insulators Arbel Haim, Roni Ilan, Jason Alicea In magnetically doped thinfilm topological insulators, aligning the magnetic moments generates a quantum anomalous Hall phase with a single chiral edge state. We study the demagnetization process and show that disorder from randomly oriented magnetic moments can produce a quantumspinHalllike phase with counterpropagating helical edge modes protected by a unitary reflection symmetry. This phase is analogous to the quantum spin Hall effect observed in the zeroth Landau level of graphene, which is also protected by a unitary symmetry (spin rotation). We show that introducing superconductivity, combined with selective breaking of reflection symmetry by a gate, allows for creation and manipulation of Majorana zero modes via purely electrical means. 
Wednesday, March 6, 2019 8:36AM  8:48AM 
K03.00004: Topological states from topological crystals Zhida Song, ShengJie Huang, Yang Qi, Chen Fang, Michael A Hermele We show that crystalline symmetry protected topological states is adiabatically connected to a realspace crystalline pattern of lowerdimensional topological states, which we refer to as a topological crystal. As a demonstration of principle, we explicitly enumerate all inequivalent topological crystals for noninteracting timereversal symmetric electronic insulators with significant spinorbit coupling and any one of the 230 space groups in three dimensions. Because every topological crystalline insulator can be deformed into a topological crystal, the enumeration of the latter gives topological crystalline insulators a full classification and for each class an explicit realspace construction. 
Wednesday, March 6, 2019 8:48AM  9:00AM 
K03.00005: Landau levels of topological surface states probed by quantum capacitance Su Kong Chong, Ryuichi Tsuchikawa, Jared Harmer, Taylor D. Sparks, Vikram V. Deshpande Threedimensional topological insulator (3D TI) is known by its unique Dirac dispersion surface states arising from band inversion of its bulk. Development of discrete Landau levels (LLs) in strong perpendicular magnetic field provides strong evidence of quantization from twodimensional nature of the topological surface states. Density of states of the surface states’ LLs can be quantitatively determined through a quantum capacitance measurement. However, quantum capacitance in 3D TI is relatively less explored primarily due to mixing signals from the bulk or narrow bulk bandgap such as strained HgTe. In this work, we study the quantum capacitance of a truly bulk insulating 3D TI via a TIbased van der Waals heterostructures configuration. The quantum capacitance data are compared to the quantum Hall conductance in transport. By controlling the dualgate voltages, we access the LLs from each surface states. The chemical potentials as function of charge density are extracted to quantify the LL spacings. 
Wednesday, March 6, 2019 9:00AM  9:12AM 
K03.00006: Band structure and superconductivity in Indoped topological insulator (Pb_{0.5}Sn_{0.5})_{1x}In_{x}Te probed by NMR spectroscopy BenLi Young, PingChun Tsai, Genda Gu The bulk band structure and superconductivity in the Indoped topological crystalline insulators (Pb_{0.5}Sn_{0.5})_{1x}In_{x}Te, for x = 0, 0.1, 0.2, and 0.3, have been investigated by nuclear magnetic resonance (NMR) techniques. We found that the NMR frequency shifts of ^{117}Sn, and ^{207}Pb are dominated by the spins of free charge carriers, whereas the ^{125}Te frequency shift is determined by the magnetic orbital moments of the binding electrons. By analyzing these shifts, we conclude that In substitution for 0 ≤ x ≤ 0.3 provides not just hole carriers but also lifts the chemical potential from the valence bands to the conduction bands, in consistent with the results from the electric transport measurements. The superconductivity in the x = 0.3 sample is investigated by the nuclear spinlattice relaxation rate (1/T_{1}) as a function of temperature, where a HebelSlichter coherence peak is observed near the critical temperature. This suggests that the superconducting gap in the bulk is fully opened and this feature may favor that (Pb_{0.5}Sn_{0.5})_{0.7}In_{0.3}Te is a conventional superconductor rather than a chiral pwave topological superconductor. 
Wednesday, March 6, 2019 9:12AM  9:24AM 
K03.00007: Disorderdriven phase transitions in chiralsymmetric topological insulators Jahan Claes, Taylor Hughes Chiralsymmetric topological insulators exhibit properties, such as polarization, that are robust to translationsymmetric perturbations provided the perturbations do not close the energy gap. However, it's unclear to what extent these topologically protected properties are robust to disorder, as disorder breaks the translation symmetry. Here we study a collection of 2D chiralsymmetric models with disorder using a covariant real space formula for the topological invariant. Generically, we find that the topological invariants remain precisely quantized until a critical value of disorder, at which point it smoothly decreases to zero. Furthurmore, we find that the critical disorder occurs exactly when states at the Fermi energy become delocalized. We therefore demonstrate that the topological characteristics are robust, and that in the presence of disorder the topology is protected by a mobility gap in place of an energy gap. 
Wednesday, March 6, 2019 9:24AM  9:36AM 
K03.00008: Low Temperature Terahertz Nano Imaging of WTe2 Thin Film Ran Jing, Yinming Shao, Zaiyao Fei, Xiaodong Xu, Dimitri Basov We discuss the development of cryogenic scanning nearfield microscope suitable for nanoscale imaging and spectroscopy at terahertz frequency range with the spatial resolution below 130 nm[1]. We report terahertz nearfield measurement of WTe2 thin film of 1 to 3 layers[2] above and below the metalinsulator transition. Clear contrast in nearfield signal can be observed among regions with different layer numbers and between metallic and insulating state. 
Wednesday, March 6, 2019 9:36AM  9:48AM 
K03.00009: Detection of higher order topological phase in a disordered breathing Kagome model by using machine learning Hiromu Araki, Tomonari Mizoguchi, Yasuhiro Hatsugai A higher order topological insulator is a new concept of topological states of matter, which is characterized by the emergent boundary states whose dimensionality is lower by more than two compared with that of the bulk, and draws a considerable interest. Yet, its robustness against disorders is still unclear. Here we investigate a phase diagram of higher order topological insulator phases in a breathing Kagome model in the presence of disorders, by using a stateoftheart machine learning technique. We find that the corner states survive against the finite strength of disorder potential as long as the energy gap is not closed, indicating the stability of the higher order topological phases against the disorders. We also discuss the relation between the higher order topological phase and the Z_3 Berry phase, which is a bulk topological invariant. 
Wednesday, March 6, 2019 9:48AM  10:00AM 
K03.00010: Doublefrequency AharonovBohm effect and nonAbelian braiding property of JackiwRebbi zeromode Yijia Wu, Jie Liu, Haiwen Liu, Hua Jiang, Xincheng Xie Ever since its first proposal in 1976, JackiwRebbi zeromode has been drawing extensive attention for its charming properties including charge fractional quantization, topologically protected zeroenergy and possible nonAbelian statistics. We numerically investigate the JackiwRebbi zeromode in a quantum spin Hall insulator heterostructure and show that its zeroenergy nature leads to a doublefrequency AharonovBohm effect in electronic transport. Such observation suggests that Majorana zeromode could be viewed as a special case of JackiwRebbi zeromode. Moreover, similar to the Majorana zeromodes, JackiwRebbi zeromodes also show nonAbelian braiding properties in a crossshaped junction. However, such nonAbelian property can be destroyed by infinitesimal disorder breaking chargeconjugation symmetry, implying the presence of chargeconjugation symmetry is of equal importance as the topological gap in the topological quantum computation. 
Wednesday, March 6, 2019 10:00AM  10:12AM 
K03.00011: Quasiparticle Interference on the Step Edges of Epitaxial Stanene on InSb (111) Jianfeng Zhang, Xiaohu Zheng, RuiRui Du Stanene (singlelayer of tin), having an atomic structure similar to graphene, offers a promising platform for achieving roomtemperature quantum spin Hall effect with a gap of 0.3 eV [13]. We have performed the insitu scanning tunneling microscopy experiments on stanene which was epitaxially grown on the InSb (111). Several types of step edges have been observed in the atomicresolution STM topographic image. The quasiparticle interference near the steps has been detected by STS, allowing us to study the electron scattering behavior along the edge in relation to the topological property of the edge state. 
Wednesday, March 6, 2019 10:12AM  10:24AM 
K03.00012: Experimental demonstration of the robustness of topological surface states on a PbTaSe_{2} superconductor Hao Zheng, Shuang Jia, Hsin Lin, Zahid Hasan Conventional semiconductor electronic surface states are determined by the details of its surface geometry, and the chemical nature of the surface atoms. Conversely, topological surface states arise entirely from the nontrivial bulk band topology. In topological insulators, the bulk electronic structure is always gapped while the surface is metallic everywhere independent of surface details. This bulkboundary correspondence is the key manifestation of topology in a condensed matter system. 

K03.00013: ABSTRACT WITHDRAWN

Wednesday, March 6, 2019 10:36AM  10:48AM 
K03.00014: Chiral Phonon Transport Induced by Topological Magnons Even Thingstad, Akashdeep Kamra, Arne Brataas, Asle Sudbo The plethora of recent discoveries in the field of topological electronic insulators has inspired a search for boson systems with similar properties. There are predictions that ferromagnets on a twodimensional honeycomb lattice may host chiral edge magnons. In such systems, we theoretically study how magnons and phonons couple. We find topological magnetopolarons around the avoided crossings between phonons and topological magnons. Exploiting this feature along with our finding of Rayleigh edge phonons in armchair ribbons, we demonstrate the existence of chiral edge modes with a phononic character. We predict that these modes mediate a chirality in the coherent phonon response and suggest to measure this effect via elastic transducers. These findings reveal a possible approach towards heat management in future devices. 
Wednesday, March 6, 2019 10:48AM  11:00AM 
K03.00015: Firstorder topological quantum phase transitions in strongly correlated onedimensional systems Simone Barbarino Topological quantum phase transitions, such as the transition between a topological insulator and a trivial gapped phase, are hallmarked by the 
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