Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y45: Topological Insulators: Theory IIILive

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Sponsoring Units: DCMP Chair: Aris Alexandradinata, University of Illinois at UrbanaChampaign 
Friday, March 19, 2021 11:30AM  11:42AM Live 
Y45.00001: Topological Quantum Chemistry on Phonon Spectra: An Application to the Buckled Honeycomb Lattice Martin Gutierrez, Maia Garcia Vergniory, Ion Errea, Juan Luis Mañes Recently the systematic application of the methods of Topological Quantum Chemistry (TQC) [1] has enormously enlarged the number of known topological materials [2] and led to new and more refined methods of classifying their topology. 
Friday, March 19, 2021 11:42AM  11:54AM Live 
Y45.00002: Catalogue of Flat Band Stoichiometric Materials Mingrui Li, Yuanfeng Xu, DaShuai Ma, Luis Elcoro, Zhida Song, Nai Phuan Ong, Stuart Parkin, Claudia Felser, Ali Yazdani, Robert Cava, Andrei B Bernevig, Nicolas Regnault We present a complete catalogue of the stoichiometric materials with flat bands around the Fermi level that exist in nature and filter out all the materials with linegraph (sub)lattice. By scanning the materials in the Topological Materials database, which contains the band structures of all ICSD materials with less than 80 atoms per unit cell, we identify the compounds that exhibit several degrees of band flatness on a significant fraction of the Brillouin zone. Among these materials, we identify the ones with topological flat bands in the specified energy window. By analyzing the crystal structures with symmetry groups, we perform a highthroughput search for materials, whose chemical elements are located at centers that form (either partial or full) 2D/3D line graph lattices. Besides, we also perform a corresponding preliminary classification of the materials with bipartite sublattice with different atoms in the two sublattices, whose band structure hosts nontrivial flat bands. We further perform a manual curation of the flatband database to select the materials with the best extended flat bands and select several representative materials and explain the origin of the flat bands presented. 
Friday, March 19, 2021 11:54AM  12:06PM Live 
Y45.00003: Thermoelectric Transport and Shock Dynamics in Helical Edge States Xinghai Zhang, Matthew Foster We study transport and shock dynamics in onedimensional helical liquids via chiral hydrodynamics. Helical liquids can arise as edge states of 2D Z2 topological insulators, hinge states of higherorder topological phases, in graphene under strong magnetic fields, and in quantum wires with strong spinorbit coupling. We focus on an unusual timereversal invariant oneparticle umklapp (1PU) scattering mechanism enabled by Rasha spinorbit coupling. Transport coefficients demonstrate the crossover between ballistic and hydrodynamic behavior. Moreover, we show that shock fronts develop due to the 1PU scattering for counterpropagating charge packets induced by an intense electric pulse. The 1PU scatterings convert rightmovers at the hot leading edge of a rightmoving packet into leftmovers and cool them down. The slope of the density at the shock front increases in time and goes to infinity at long times. The effect is enhanced by stronger 1PU interactions and the shock front can form faster for strong interactions. 
Friday, March 19, 2021 12:06PM  12:18PM Live 
Y45.00004: Jacutingaitefamily: a class of 2D topological materials Felipe Crasto de Lima, Roberto Hiroki Miwa, ADALBERTO FAZZIO Jacutingate, a recently discovered Brazilian naturally occurring mineral, has shown to be the first experimental realization of the KaneMele topological model. Such a system (Pt_{2}HgSe_{3}) presents a similar structure with the transition metal dichalcogenides (TMD) 1T phase, where 1/4 of the Se atoms are replaced by Hg. In this work, based on the stability of other TMDs, we have unveiled a class of materials M_{2}NX_{3} (M =Ni, Pt, Pd; N =Zn, Cd, Hg; and X=S, Se, Te), sharing jacutingaite’s 
Friday, March 19, 2021 12:18PM  12:30PM Live 
Y45.00005: Dc Electrical Current Generated by Upstream Neutral Modes Ankur Das, Sumathi Rao, Yuval Gefen, Ganpathy N Murthy We consider a setup made of a chiral charged edge mode and two counterpropagating neutral modes near the boundary of a quantum Hall edge. The charge mode is decoupled (tunnelingwise and interactionwise) from the latter throught out most of the edge. These modes interact near the electrically active contact which they are tunnel coupled. We show that injecting downstream electrical current in the charge mode may result in a d.c. current measured in an upstream contact. Our conceptual setup may be realized with a simple edge mode of a quantum Hall phase, and a quasi 1d XXZ spin chain. 
Friday, March 19, 2021 12:30PM  12:42PM Live 
Y45.00006: Experimental Demonstration of Dynamic Topological Pumping Across Incommensurate Bilayered Acoustic Metamaterials Wenting Cheng, Emil Vasile Prodan, Camelia Prodan In this talk, we present a system of acoustic metamaterials generated by incommensurate bilayers with a phason degree of freedom. The system presents dynamic energy transfer in adiabatic cycles across the crystal via pumping of topological edge modes without any outside intervention or assistance. The system is characterized experimentally by standard acoustic measurements, and via a finite element approach utilizing COMSOL Multiphysics. The experimental results and simulations confirm the energy transfer via topological pumping process. This study suggests possible applications of electron pumping in conventional insulators. 
Friday, March 19, 2021 12:42PM  12:54PM Live 
Y45.00007: Layer Correlated Phase in Double Layer Graphene at Δν=0 Amartya Saha, Ankur Das The question of the bulk phase of a quantum Hall system at the half filling is a very old and interesting one. In the recent advancement in Graphene material it is possible to create a double layer system of Graphene without interlayer tunneling. In these systems the filling fraction of each layer (ν_{1} and ν_{2}) can be controlled independently [1]. In this work we restrict the Hamiltonian using simple symmetry arguments. We study the ground state of this system in the HartreeFock approximation at Δν(=ν_{1}ν_{2})=0=ν_{1}=ν_{2} (similar to what has been done for monolayer Graphene [2]). In addition to the phases found in [2] we found the existence of layer correlated phases. 
Friday, March 19, 2021 12:54PM  1:06PM Live 
Y45.00008: Topological phases in quasiperiodic spin chains yifei liu, Lea Santos, Emil Vasile Prodan In [Y. Liu et al., arXiv:2009.03752], we investigate topological phases in quasiperiodic spinchain models and their bulkboundary principles by numerical and Ktheoretic methods. In the uncorrelated case with magnetization M=1,2, and 3, the observed chiral bands indicate that the spectral gaps are topological and Ktheoretic labels enable us to match the first Chern number with the numbers of topological edge modes. When the interaction is introduced, the robust topological edge modes are found to be strongly shaped by the interaction and, generically, they have hybrid edgelocalized and chaindelocalized structures. The bulkboundary correspondence of the interacting model is studied in [Y. Liu et al., arXiv:2010.06171]. In this work, we generate topological phases at finite magnetization densities that carry the first Chern numbers. We conclude that the nondegenerate character of a ground state carrying a nontrivial Chern number is destroyed when open boundary conditions are used. Based on those findings, we are able to generate high throughput of topological correlated states at finite densities. 
Friday, March 19, 2021 1:06PM  1:18PM Live 
Y45.00009: ThreeDimensional Real Space Invariants and Obstructed Atomic Insulators: Catalogues and Applications Yuanfeng Xu, Luis Elcoro, Zhida Song, Juan Luis Mañes, Maia Garcia Vergniory, Nicolas Regnault, Stuart Parkin, Claudia Felser, Andrei B Bernevig Topologically trivial Insulators come into two kinds: Atomic, where the Wannier centers are localized on the atoms, and obstructed atomic, where the Wannier centers are located away from the atoms. The latter, which can exhibit interesting interface states with much larger gaps than the topological insulators, have so far not been classified in 3dimensions (3d). Here, we develop the 3d real space invariants with band representations in 1651 Shubnikov space groups, which include 230 paramagnetic and 1421 magnetic space groups. By applying the RSIs to all the topological trivial insulators in Topological material database (https://www.topologicalquantumchemistry.com), we obtain about 4000 paramagnetic obstructed atomic Insulators (OAI), which should exhibit surface states and filling anomalies. Combined with symmetry analysis, we further filter out hundreds of OAIs with surface topological states such as quantum spin Hall effect and fragile bands and flat bands on the top of the surface. Finally, we comment on several potential applications of the OAIs, including first and foremost, catalysis. 
Friday, March 19, 2021 1:18PM  1:30PM Live 
Y45.00010: Resonant Inelastic Xray Spectroscopy on Electric Quadrupole Insulator Sangjin Lee, Gil Young Cho One of the guiding principles that experimentally capture a topological property is bulkedge correspondence, and many studies focus on the edges by following the principle. In this study, we propose that a scattering experiment can capture the topological properties of materials which is essentially bulk property. As a representative example, we show that resonant inelastic Xray spectroscopy on an electric quadrupole insulator. At specific energy and momentum transfer, we show that the scattering amplitude should vanish or not in a trivial or topological phase by symmetry arguments. 
Friday, March 19, 2021 1:30PM  1:42PM Live 
Y45.00011: Nonadiabatic Hall effect at Berry curvature hot spot WeiYuan Tu, Ci Li, Hongyi Yu, Wang Yao Hot spot of Berry curvature is usually found at Bloch band anticrossings, where the Hall effect due to the Berry phase can be most pronounced. With small gaps, the adiabatic limit can be exceeded in a moderate electric field. Here we present a theory of nonadiabatic Hall effect, capturing nonperturbatively the across gap electronhole excitations by the electric field. We find a general connection between the field induced electronhole coherence and intrinsic Hall velocity. In coherent evolution, the electronhole coherence can manifest as a sizeable ac Hall velocity. When environmental noise is taken into account, its joint action with the electric field favors a form of electronhole coherence that is function of wavevector and field only. The Hall current has all odd order terms in field, and still retains the intrinsic role of the Berry curvature. The quantitative demonstration uses the example of gapped Dirac cones, and our theory can be used to describe the bulk pseudospin Hall current in insulators with gapped edge such as graphene and 2D MnBi2Te4. 
Friday, March 19, 2021 1:42PM  1:54PM Live 
Y45.00012: Topological phases in the TaSe3 compound SiMin Nie, Lingyi Xing, Rongying Jin, Weiwei Xie, Zhijun Wang, Fritz Prinz Based on firstprinciples calculations, we show that stoichiometric TaSe3, synthesized in space group P21/m, belongs to a threedimensional strong topological insulator (TI) phase with Z2 invariants (1; 100). The calculated surface spectrum shows clearly a single Dirac cone on surfaces, with helical spin texture at a constantenergy contour. To check the stability of the topological phase, strain effects have been systematically investigated, showing that many topological phases survive in a wide range of the strains along both the a and c axes, such as strong TI, weak TI, and Dirac semimetal phases. TaSe3 provides us an ideal platform for experimental study of topological phase transitions. More interestingly, since superconductivity in TaSe3 has been reported for a long time, the coexistence of topological phases and a superconducting phase suggests that TaSe3 is a realistic system to study the interplay between topological and superconducting phases in the future. 
Friday, March 19, 2021 1:54PM  2:06PM Live 
Y45.00013: Quantum Hall Effect in QuasiOneDimensional Weak Topological Insulator Tianyi Xu, Patrick Cheung, Fengcheng Wu, Fan Zhang Prototypical weak topological insulators (WTI) have been theoretically predicted to be realized in quasionedimensional materials Bi_{4}X_{4 }(X = Br, I)_{ }[PRL 116, 066801 (2016)] and then experimentally confirmed in ARPES [Nature (London) 566, 518 (2019)]. The unique surface states of such a WTI have two entangled Dirac cones with strong anisotropy. We study theoretically the integer quantum Hall effect of such WTI surface states and show the important roles played by the special geometry, symmetry, topology, and their interplay in Bi_{4}X_{4}. We also predict prominent signatures in transport experiments. 
Friday, March 19, 2021 2:06PM  2:18PM On Demand 
Y45.00014: Twisted Quadrupole Topological Photonic Crystals Zhou XiaoXi Topological manipulation of waves is at the heart of cuttingedge metamaterial research. Quadrupole topological insulators were recently discovered in 2D fluxthreading lattices that exhibit higherorder topological wave trapping at both the edges and corners. Photonic crystals (PhCs), lying at the boundary between continuous media and discrete lattices, however, are incompatible with the present quadrupole topological theory. Here, quadrupole topological PhCs triggered by a twisting degreeoffreedom are unveiled. Using a topologically trivial PhC as the motherboard, it is shown that twisting induces quadrupole topological PhCs without fluxthreading. The twistinginduced crystalline symmetry enriches the Wannier polarizations and leads to the anomalous quadrupole topology. Versatile edge and corner phenomena are observed by controlling the twisting angles in a lateral heterostructure of 2D PhCs. This study paves the way toward topological twist photonics as well as the quadrupole topology in the quasicontinuum regime for phonons and polaritons. 
Friday, March 19, 2021 2:18PM  2:30PM On Demand 
Y45.00015: Theory for the chargedensitywave mechanism of 3D quantum Hall effect Fang Qin, Shuai Li, Zongzheng Du, Chunming Wang, Wenqing Zhang, Dapeng Yu, Haizhou Lu, X. C. Xie The chargedensitywave (CDW) mechanism of the 3D quantum Hall effect has been observed recently in ZrTe5 [Tang et al., Nature 569, 537 (2019)]. Quite different from previous cases, the CDW forms on a 1D band of Landau levels, which strongly depends on the magnetic field. However, its theory is still lacking. We develop a theory for the CDW mechanism of 3D quantum Hall effect. The theory can capture the main features in the experiments. We find a magnetic field induced secondorder phase transition to the CDW phase. We find that electronphonon interactions, rather than electronelectron interactions, dominate the order parameter. We extract the value of electronphonon coupling constant from the nonOhmic IV relation. We point out a commensurateincommensurate CDW crossover in the experiment. More importantly, our theory explores a rare case, in which a magnetic field can induce an orderparameter phase transition in one direction but a topological phase transition in other two directions, both depend on one magnetic field. It will be useful and inspire further experiments and theories on this emergent phase of matter. 
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