Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K64: Correlated Topological StatesRecordings Available

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Sponsoring Units: DCMP Chair: Arpit Arora, Nanyang Technological University Room: Hyatt Regency Hotel Grant Park B 
Tuesday, March 15, 2022 3:00PM  3:12PM 
K64.00001: Nonlinear response in Mott Insulators Sayantan Roy, Zachariah M Addison, Nandini Trivedi We develop a new formalism to calculate linear and nonlinear response functions for a Mott insulator, with and without spin orbit coupling. We consider the effects of an external frequency dependent gauge field, within minimal coupling, on the fermionic degrees of freedom in the repulsive Fermi Hubbard model. This formalism is necessary for large onsite Hubbard interactions, since localized spin moments do not couple to an external electric field. We calculate the nonlinear photogalvanic effect and second harmonic generation, that are sensitive to underlying symmetries of materials. Our formalism allows us to highlight experimental signatures of symmetries and topology in spin orbit induced frustrated systems through the structure of the response tensors. 
Tuesday, March 15, 2022 3:12PM  3:24PM 
K64.00002: A universal tripartite entanglement signature of ungappable edge states Karthik Siva, Yijian Zou, Tomohiro Soejima, Roger Mong, Michael P Zaletel Gapped twodimensional topological phases can feature ungappable edge states which are robust even in the absence of protecting symmetries. In this work we show that a multipartite entanglement measure recently proposed in the context of holography, the Markov gap, provides a universal diagnostic of ungappable edge states. Defined as a difference of the reflected entropy and mutual information $h(A:B) = S_R(A:B)  I(A:B)$ between two parties, we argue that for $A,B$ being adjacent subregions in the bulk, $h=\frac{c_+}{3}\log 2$, where $c_+$ is the minimal total central charge of the boundary theory. As evidence, we prove that $h=0$ for stringnet models, and numerically verify that $h=\frac{C}{3}\log 2$ for a Chern$C$ insulator. Our work establishes a unique bulk entanglement criteria for the presence of a conformal field theory on the boundary. 
Tuesday, March 15, 2022 3:24PM  3:36PM 
K64.00003: Continuously varying infinite randomness in the disordered XYZ spin chain Brenden Roberts, Olexei I Motrunich We study a critical line between localized magnetic phases in the XYZ spin chain with quenched randomness, where a previous strongdisorder RG calculation, assuming marginal MBL, suggested continuously varying critical indices. We do not address the question of MBL but instead solve the lowenergy physics using a new unbiased tensor network method. These results are consistent with a line of infinite randomness fixed points. For weak interactions, a selfconsistent Hartree–Focktype treatment captures much of the important physics, including continuously varying exponents. Using a strongdisorder RG based on random walks, we show that local correlation induced between the meanfield couplings is a strictly marginal perturbation. This constitutes an example of a line of fixed points with continuously varying exponents in the equivalent disordered freefermion chain. We argue that this line of fixed points also controls the critical XYZ spin chain for finite interactions. 
Tuesday, March 15, 2022 3:36PM  3:48PM 
K64.00004: Local structure memory effects in the polar and nonpolar phases of MoTe_{2} Valeri Petkov Materials exhibiting reduced dimensionality and strongly interacting charge and lattice degrees of freedom, such as layered transition metal dichalcogenides, can appear in various atomic structure states that harbor fascinating quantum phenomena. The complexity of the states, however, often makes it challenging to identify the nature of the observed phenomena, impeding their exploration for practical applications. We show that the problem can be alleviated by using highenergy xray diffraction coupled to atomic pair distribution function analysis. In particular, using this nontraditional technique, we find that whereas, macroscopically, the reversible transition between the polar 1T’ and nonpolar T_{d} phases of MoTe_{2 }is firstorder, locally, it is not. A great deal of the stacking sequence of TeMoTe layers characteristic to the polar 1T’ phase persists locally in the nonpolar T_{d} phase, and vice versa, over a broad temperature range extending about 100 K both below and above the transition. The presence of coexisting local polar and nonpolar regions and the resulting variety of internal interfaces where the spatial inversion symmetry is broken may be behind some of the unusual electronic properties of T_{d}MoTe_{2}, including its putative typeII Weyl semimetal state. 
Tuesday, March 15, 2022 3:48PM  4:00PM 
K64.00005: Robustness of Kitaev Honeycomb Ground State in Presence of a Quench Wesley Roberts, Michael Vogl, Gregory A Fiete Motivated by the importance of stability of quantum computation against perturbations and external noise, we study the Kitaev honeycomb model, a system of interest for topological quantum computing, when it is subjected to different quenches. Particularly, we put our focus on the longtime behaviors of the Loschmidt echo and Uhlmann fidelity for the Kitaev ground state when the system is subjected to a uniform magnetic field and local impurities. We compare the cases without and with noise. We focus on Gaussian white noise modelled by a Lindblad Master Equation approach. We find that in the gapped phase, the Kitaev ground state is robust to perturbations, further motivating the potential usefulness of a gapped Kitaevlike system in quantum computing. This result stands in contrast to the other cases we study where we find an exponential decay that appears to be a manifestation of the orthogonality catastrophe. 
Tuesday, March 15, 2022 4:00PM  4:12PM 
K64.00006: Viscous electron magnetotransport properties near charge neutrality Songci Li, Anton Andreev, Alex Levchenko We focus on a magnetohydrodynamic electron transport theory in conductors lacking Galilean invariance in the presence of long range disorder. We obtain perturbative results of transport coefficients for weak disorder and show their dependences on the intrinsic transport coefficients of the electron liquid and the correlation function of the disorder potential. At charge neutrality, the electron transport is strongly affected by the vortical hydrodynamic flow caused by the local charge densities, as opposed to the potential flow away from charge neutrality. We then apply our results to graphene near charge neutrality. In particular, we show that the magnetoresistance is positive and quadratic in weak magnetic field. The Hall resistivity is given by the classical Hall resistivity with a renormalization factor depending on the doping density, correlation function of the disorder potential and the shear viscosity. We also study magnetothermal transport coefficients. We show that the magnetothermal conductivity is negative and quadratic in field. We also show the viscous and disorder effects for the Nernst coefficient and magnetothermal power. 
Tuesday, March 15, 2022 4:12PM  4:24PM 
K64.00007: The boundary of 2+1D fermionic topological orders ChangHan Chen, XiaoGang Wen We propose a systematic approach to investigate the boundary of 2+1D abelian fermionic topological orders, in which S and T matrices are not welldefined. The trick is to realize the fermionic system "on the top" of the Z2 topological order, motivated by the hierarchical construction of fractional quantum Hall states. We explicitly show the construction of the K matrix as well as the correspondence between equivalence classes of excitations. Within the new framework, we describe the gapped boundaries via modular covariant partition functions straightforwardly. Yet, some subtleties have to be considered when we convert the solutions back to the original fermionic systems. An algorithm to find such partition functions is also discussed. Along the way, we raised a conjecture, "S+T2 always have a rational basis." 
Tuesday, March 15, 2022 4:24PM  4:36PM 
K64.00008: Discovery of a new topological phase in the anisotropic Kitaev model with field Cullen Gantenberg, Shi Feng, Nandini Trivedi The Kitaev model with anisotropic interactions on the bonds of a honeycomb lattice is a paradigmatic model for quantum spin liquids. Aside from the gapless and gapped phases of the original model, more phases are revealed by the addition of a nonperturbative magnetic field. For example, the fieldinduced U(1) QSL phase with isotropic bonds (Kz=K) has been studied in both theory and experiments. We explore the effects of adding a magnetic field on Kitaev interactions away from the isotropic point (Kz≠K), and discover a new gapped topological phase that has eluded detection by calculations using local order parameters (e.g. susceptibility). The topological nature of this phase is reflected in (i) the emergent ground state degeneracy and (ii) the nontrivial topological entanglement entropy. 
Tuesday, March 15, 2022 4:36PM  4:48PM 
K64.00009: Arboreal Topological and Fracton Phases Vijay B Shenoy, Nandagopal Manoj We investigate topologically ordered and fracton ordered states on arenas that do not have an underlying manifold structure. We focus on arenas built from tree graphs, such as the kcoordinated Bethe lattice B(k) and a hypertree called the (k,n)hyperBethe lattice HB(k,n) consisting of kcoordinated hyperlinks (defined by n sites), to construct ``multidimensional arboreal arenas'' using the notion of the generalized graph cartesian product □. We study various quantum systems such as the Z_{2} gauge theory, generalized quantum Ising models (GQIM), the fractonic Xcube model, and related Xcube gauge theory defined on these arenas. Even the simple Z_{2} gauge theory has a fractonic character on an arboreal arena  the monopole excitation is fully immobile. Similarly, the Xcube model on a 3dimensional arboreal arena is also fully fractonic as all multipoles are immobile. Next, we find an intriguing class of dualities in arboreal arenas: e.g. the Z_{2} gauge theory defined on B(k_{1})□B(k_{2}) is dual to a GQIM defined on HB(2,k_{1})□HB(2,k_{2}). Finally, we demonstrate, using entanglement renormalization, that there are only three classes of arboreal toric code topological orders on twodimensional arboreal arenas, and four distinct arboreal Xcube fracton orders on 3d arboreal arenas. 
Tuesday, March 15, 2022 4:48PM  5:00PM 
K64.00010: Predicted photoinduced topological phases in organic salt α(BEDTTTF)_{2}I_{3} Keisuke Kitayama, Masahito Mochizuki Photoinduced phase transitions are attracting intensive interest recently. Many theoretical studies have been conducted using the Floquet theory since pioneering work by Oka and Aoki which theoretically predicted the photoinduced topological phase transition in graphene. However, for further development of this growing field, proposals of novel target materials and predictions of interesting physical phenomena from theoretical side are eagerly anticipated. Under these circumstances, we theoretically predicted the occurrence of photoinduced topological phase transition in the organic salt α(BEDTTTF)_{2}I_{3} under irradiation with circularly polarized light. By analyzing band structures, Chern numbers, and Hall conductivity in a photoirradiated system, we obtain a rich nonequilibrium phase diagram in plane of the amplitude and frequency of light, which includes Chern insulator, nontopological insulator, and semimetal phases. In addition, calculations of the Hall conductivity using the FloquetKeldysh formalism predicted that the quantization of Hall conductivity can be observed also in this photoinduced Chern insulator phase. These results widen a range of target materials and contribute to the development of research for the optical manipulation of electronic states in matters. 
Tuesday, March 15, 2022 5:00PM  5:12PM 
K64.00011: Infrared conductivity of LaSb : evidence for noncompensation origin of extreme magnetoresistance. HyunDon Kim, Eunjip Choi, Jiho Kim, Dmitry Smirnov, JongSoo Rhyee, WonHyuk Shon, Yong Seung Kwon, Kwangnam Yu, Seongphill Moon Extremely large and unsaturating magnetoresistance (XMR) is an unprecedented phenomenon discovered in topological semimetals. Vast amount of works so far attributed XMR to perfect or nearperfect compensation of electrons and holes that assumed their carrier densities are equal. Here we performed infrared reflectance measurement as well as dctransport on single crystal LaSb. The data show two Drude peaks with drastically different scattering rates. We determine (n, γ) for the hole and electron from the two Drude peaks and use them to calculate magneticdependent longitudinal resistivity ρ_{xx}(B) which shows an excellent agreement with measured ρ_{xx}(B) for wide range of, 13T<B<13T, the carrier densities for hole and electron differ by about factor 2. This result shows that the large difference of scattering rates leads to XMR, and perfect charge compensation is not the exclusive origin. 
Tuesday, March 15, 2022 5:12PM  5:24PM 
K64.00012: Realizing RiceMele model on Floquet lattice Haru K Park, Junmo Jeon, SungBin Lee Finding topological properties in timeperiodic Hamiltonian has focused physicists more than decades. The celebrated RiceMele model is a wellknown nontrivial timeperiodic Hamiltonian, whose topological invariant represents the amount of charge pump. In our research, we construct a Floquet system with multiple frequencies which has similar analogy with RiceMele model. This system changes the role of position and time in RiceMele model into frequency and momentum respectively, and can be realized by simply tuning the direction of timeperiodic magnetic field on a singlespin system. We also address the physical evidence of the protected topological number obtained by measuring the mean phase velocity of the spin state. 
Tuesday, March 15, 2022 5:24PM  5:36PM 
K64.00013: Incoherent topological insulator close to the Mott transition in honeycomb materials. Manuel Fernandez Lopez Motivated by the anomalous metallic properties observed in many strongly 
Tuesday, March 15, 2022 5:36PM  5:48PM 
K64.00014: Renyi entropies and negative central charges in nonHermitian quantum systems YiTing Tu, YuChin Tzeng, PoYao Chang Quantum entanglement is one essential element to characterize manybody quantum systems. However, so far, the entanglement measures mainly restrict to Hermitian systems. Here, we propose a natural extension of entanglement and Rényi entropies to nonHermitian quantum systems. We demonstrate the generic entanglement and Rényi entropies capture the correct entanglement properties in nonHermitian critical systems, where the lowenergy properties are governed by the nonunitary conformal field theories (CFTs). We find excellent agreement between the numerical extrapolation of the negative central charges from the generic entanglement/Rényi entropy and the nonunitary CFT prediction. Furthermore, we apply the generic entanglement/Rényi entropy to symmetryprotected topological phases with nonHermitian perturbations. We find the generic nth Rényi entropy captures the expected entanglement property, whereas the traditional Rényi entropy can exhibit unnatural singularities due to its improper definition. 
Tuesday, March 15, 2022 5:48PM  6:00PM 
K64.00015: Nonlinear response functions and disorder: the case of the photo galvanic effect Konstantinos Ladovrechis, Tobias P Meng The circular photogalvanic effect (CPGE) is a nonlinear photocurrent which is generated in materials with broken inversion symmetry when they are shed with circularly polarised light. In Weyl semimetals, the CPGE is quantized in terms of fundamental constants and the Chern numbers associated with the Weyl nodes. In this work, we investigate the effect of pointlike disorder onto the quantization of CPGE. Implementing 1storder and selfconsistent Born approximations, we identify that the quantization of CPGE is broken and perturbative corrections in the scattering strength emerge, which we further classify in terms of selfenergy and vertex corrections. 
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