Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Q30: Strongly Correlated Systems, Including Quantum Fluids and Solids XIV |
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Sponsoring Units: DCMP Chair: Shuang Tang, SUNY Polytechnic Institute Room: Room 222/223 |
Wednesday, March 8, 2023 3:00PM - 3:12PM |
Q30.00001: Anomalous Quantum Hall Bilayer Effect Gurjyot S Sethi, Feng Liu Quantum Hall bilayers (QHB) are two-component fractional quantum Hall (FQH) systems that provide a unique platform to realize exotic Abelian/non-Abelian FQH and excitonic condensate states, but in the presence of a high magnetic field. Here, we show that these states can be realized in an analog of bilayer Kagome lattice with flat bands (FBs) in each layer, leading to anomalous quantum Hall bilayer effect, without magnetic field. Using exact diagonalization of finite size bilayer Kagome lattices, we demonstrate the stabilization of excitonic condensate Halperin's (1,1,1) and (3,3,3) state at the total filling and of the two FBs, respectively. We further show that by tuning the interlayer tunneling at , one can expect a phase transition from Halperin's (3,3,0) state to particle-hole conjugate of Laughlin's 1/3 state, as previously observed in QHB systems. Our work significantly enriches the field of FB physics by demonstrating bilayer FB systems as an attractive avenue for realizing exotic QHB states without magnetic field. |
Wednesday, March 8, 2023 3:12PM - 3:24PM |
Q30.00002: Coupled topological flat and wide bands: Quasiparticle formation and destruction Lei Chen, Qimiao Si, Shouvik Sur, Fang Xie, Haoyu Hu Flat bands amplify the effects from correlations. Lattices with destructive kinematic interference provide natural platforms to explore both topology in correlated settings and correlation physics enriched by topology. Recent experiments in correlated kagome metals have found evidence for strange-metal behavior. A major theoretical challenge is to study the effect of local Coulomb repulsion when the band topology obstructs a real-space description. Here [1,2], we study a model with topological flat bands coupled with dispersive wide bands. Exponentially localized Wannier functions are constructed, which leads to a Kondo lattice description. We identify an orbital-selective Mott transition from the effective model and characterize the Kondo-driven quasiparticles and their destruction. We systematically address the conditions under which the orbital-selective Mott transition takes place. Our work provides a conceptual framework to address the strange-metal behavior in kagome metals and beyond. |
Wednesday, March 8, 2023 3:24PM - 3:36PM |
Q30.00003: Self-correction from higher-form symmetry protection on a boundary Charles N Stahl Recent work has shown that a self-correcting memory can exist in 3 spatial dimensions, provided it is protected by a 1-form symmetry. Requiring that a system's dynamics obey this type of symmetry is equivalent to enforcing a macroscopic number of symmetry terms throughout the bulk. In this talk, I will show how to replace the explicit 1-form symmetry in the bulk with an emergent 1-form symmetry. Although the symmetry still has to be explicitly enforced on the boundary, this only requires O(L^2) terms instead of O(L^3) terms. I will then reinterpret this boundary as a symmetry-protected topological defect in a bulk topological order. |
Wednesday, March 8, 2023 3:36PM - 3:48PM |
Q30.00004: Light-Matter Interactions of Wannier-Obstructed Correlated Quantum Materials Wai Ting Tai, Martin Claassen Two-dimensional moiré heterostructures and interacting flat bands have recently emerged as strongly correlated electron systems with geometric obstructions to the formation of well-localized Wannier functions. Much of the interesting properties of such systems can be revealed from their low-frequency optical responses; however, while these should in principle be dictated by the low-energy dynamics of correlated electrons, isolating the low-energy bands of the light-matter-coupled Hamiltonian can easily violate gauge invariance. Here, we present a quantum geometric interpretation of this violation and the subsequent failure of conventional velocity gauge calculations. We provide a new prescription that factors in geometrical effects via additional Berry phase contributions that couple photons to both electron kinetics and electronic interactions. The mechanism is demonstrated on a strongly interacting 1D chain with emergent bond density wave order, which hosts a flat symmetry-protected topological band with tunable Wannier function spread. We show that our theory faithfully captures its full non-equilibrium dynamics for low-frequency optical driving fields and presents a quantum geometric interpretation of its linear and non-linear THz optical responses. Applications of the theory to two-dimensional quantum materials will be discussed. |
Wednesday, March 8, 2023 3:48PM - 4:00PM |
Q30.00005: Valley-coherent quantum anomalous Hall state in AB-stacked MoTe2/WSe2 bilayers Zui Tao, Bowen Shen, Shengwei Jiang, Tingxin Li, Lizhong Li, Liguo Ma, Wenjin Zhao, Jenny Hu, Kateryna Pistunova, Kenji Watanabe, Takashi Taniguchi, Tony F Heinz, Kin Fai Mak, Jie Shan Moire´ materials provide fertile ground for the correlated and topological quantum phenomena. Among them, the quantum anomalous Hall (QAH) effect, in which the Hall resistance is quantized even under zero magnetic field, is a direct manifestation of the intrinsic topological properties of a material and an appealing attribute for low-power electronics applications. The QAH effect has been observed in both graphene and transition metal dichalcogenide (TMD) moire´ materials. It is thought to arise from the interaction-driven valley polarization of the narrow moire´ bands. Here, we show surprisingly that the newly discovered QAH state in AB-stacked MoTe2/WSe2 moire´ bilayers is not valley-polarized but valley-coherent. The layer- and helicity-resolved optical spectroscopy measurement reveals that the QAH ground state possesses spontaneous spin (valley) polarization aligned (anti-aligned) in two TMD layers. In addition, saturation of the out-of-plane spin polarization in both layers occurs only under high magnetic fields, supporting a canted spin texture. Our results call for a new mechanism for the QAH effect and highlight the potential of TMD moire´ materials with strong electronic correlations and spin-orbit interactions for exotic topological states. |
Wednesday, March 8, 2023 4:00PM - 4:12PM |
Q30.00006: Giant magnetoresistance across the magnetic-field induced semiconductor-semimetal transition in half-Heusler HoAuSn Kentaro Ueda, Motoaki Hirayama, Ryo Kurokawa, Tonghua Yu, Hiraku Saito, Taro Nakajima, Markus Kriener, Manabu Hoshino, Daisuke Hashizume, Taka-hisa Arima, Yoshinori Tokura The discovery of topological insulators and semimetals in zinc-blend HgTe and its relatives generates strong activity in building contemporary material science. Ternary half-Heusler compounds, which are not only related to the zinc-blends electronically but involve magnetic rare-earth ions, have served as an ideal platform to explore next-generation multifunctional topological states. However, most of them reported so far were band-inverted zero-gap semiconductors RPtBi and RPdBi. |
Wednesday, March 8, 2023 4:12PM - 4:24PM |
Q30.00007: An Interaction Bulk-Boundary Relation and its Applications Towards Symmetry Breaking and Beyond Saran Vijayan, Fei Zhou Topological insulators are materials known to possess robust boundary states whose low energy excitations resemble half of the massless Dirac fermions, with the other half being localized at the opposite boundary. Hence, an attractively interacting topological surface naturally results in a topological superconducting phase (TSC) that hosts emergent Majorana fermions. In addition, phase transitions between the semi-metallic phase and the superconducting phase of the surface states have an emergent (2+1) D Supersymmetry. In this respect, we studied the interactions between topological surface matter. We put forward a simple scaling relation that connects interactions between gapped bulk topological matter and gapless surface fermions which we have named 'the interacting bulk-boundary (BBR) relation'. Using the BBR phenomenology we developed, we propose that the attractive phonon-mediated interaction between electrons is greatly enhanced if one chooses a topological material such that its bulk energy gap matches its Debye frequency. As an application, we propose a semi-realistic approach to realize attractively interacting electronic ground states on topological surfaces. |
Wednesday, March 8, 2023 4:24PM - 4:36PM |
Q30.00008: Quantum geometry, particle-hole asymmetry and their applications in moiré materials with flat dispersion Kang Yang, Ahmed Abouelkomsan, Emil J Bergholtz Topological bands with a flat dispersion host strongly correlated states with or without intrinsic topological orders. The kinetic part of the system is trivial and the system is dominated by the interaction. At a first glance, electrons do not have any preference to occupy in the Brillouin zone. Despite the featureless kinetic dispersion, topological bands are usually equipped with nontrivial band geometry. We show that the nonuniform band geometry gives rise to emergent Fermi surfaces and it leads to a general particle-hole asymmetry. The electrons tend to fill regions in the Brillouin zone where their quantum distance is shorter. The emergent Fermi surface transforms the strongly interacting problem to a weakly interacting one. This dictates the low-energy physics and serves as a guiding principle for potential symmetry-breaking states. We show that in moiré materials, the quantum distance can be well approximated by a local quantity called the quantum metric. From this simple quantity, we can deduce what phases are favoured in different moiré systems at fractional fillings. |
Wednesday, March 8, 2023 4:36PM - 4:48PM |
Q30.00009: Anomaly of $(2+1)$-Dimensional Symmetry-Enriched Topological Order from $(3+1)$-Dimensional Topological Quantum Field Theory Weicheng Ye, Liujun Zou Symmetry acting on a (2+1)$D$ topological order can be anomalous in the sense that they possess an obstruction to being realized as a purely (2+1)$D$ on-site symmetry. In this paper, we develop a (3+1)$D$ topological quantum field theory to calculate the anomaly indicators of a (2+1)$D$ topological order with a general finite group symmetry $G$, which may contain anti-unitary elements and/or permute anyons. These anomaly indicators are partition functions of the (3+1)$D$ topological quantum field theory on a specific manifold equipped with some $G$-bundle, and they are expressed using the data characterizing the topological order and the symmetry actions. Combined with the relative anomaly formalism, our framework actually enables us to calculate the anomaly of a given topological order with a fully general symmetry. Our framework is applied to derive the anomaly indicators for various symmetry groups, including $mathbb{Z}_2 imesmathbb{Z}_2$, $mathbb{Z}_2^T imesmathbb{Z}_2^T$, etc, where $mathbb{Z}_2$ and $mathbb{Z}_2^T$ denote a unitary and anti-unitary order-2 group, respectively. |
Wednesday, March 8, 2023 4:48PM - 5:00PM |
Q30.00010: How do neutral modes affect charge conductance in the ν=5/2? Mykhailo M Yutushui, Ady L Stern, David F Mross We propose an experiment to identify the topological order of the ν=5/2 state through a measurement of the electric conductance of a mesoscopic device. Our setup is based on interfacing ν=2,5/2, and 3 in the same device. Its conductance can unambiguously establish or rule out the particle-hole symmetric Pfaffian topological order, which is supported by recent thermal measurements. Additionally, it distinguishes between the Moore-Read and anti-Pfaffian topological orders, which are favored by numerical calculations. |
Wednesday, March 8, 2023 5:00PM - 5:12PM |
Q30.00011: Bulk Detection of Average Symmetry-Protected Topological Phases Through Strange Density Matrix Jianhao Zhang We demonstrate that the recently established average symmetry-protected topological (ASPT) phases can be directly detected in the bulk by the strange density matrix and the corresponding strange correlator. We obtain that even though the ASPT state as a density matrix $ ho$ we detect is short-range entangled (SRE), its strange correlator has long-range behavior if the density matrix $ ho$ is a nontrivial ASPT phase. By explicit calculations and Monte-Carlo simulations, we confirm the strange correlator detection of ASPT phases by two typical examples: (1+1)D cluster state with random disorder and (2+1)D ASPT protected by $SO(3) imesmathbb{Z}_2^{mathrm{ave}}$ and prove that the SPT phases without ``domain wall decoration'' configuration in the clean system have no ASPT counterpart by vanishing strange density matrix. We further make some connections with the correlation function of statistical models. |
Wednesday, March 8, 2023 5:12PM - 5:24PM Author not Attending |
Q30.00012: Classifation of 3D fermionic symmetry-protected topological (fSPT) phases Jingren ZHOU We study the classification of fermionic SPT (fSPT) phases in 3D via the method called three-loop braiding statistics. There is an interesting fact that each anomaly-free SPT phase can be mapped to a corresponding topological order, by a technic called “gauging the symmetry”. By fully gauging all symmetries, we obtain a topological order without any symmetry, but with topological particle-like and loop-like excitations in 3D. The particle-loop braiding process can be understood in a way analogous to the Aharonov-Bohm effect. While since loop-like excitations are topological (i.e., their mutual braiding statistics is invariant under smooth deformations of the loops), a loop-loop braiding can be equivalently transformed to a particle-loop braiding. Particle-loop and loop-loop braidings give no new information up to linear representations of the symmetry group. However, if we insert a base-loop to the two braiding loops, which forms the so-called three-loop braiding process, a loop cannot be equivalently treated as a particle anymore. And the loops with a base loop inserted now become anyons with nontrivial braiding statistics, which may even be non-Abelian. And we find that studying all three-loop braiding statistics gives a classification of all 3D fSPT phases with on-site finite unitary symmetries. Further, we explore the Majorana zero modes on loop-like excitations. We find the non-Abelian three-loop braiding statistics of them as a characteristic indicator of the Majorana chain decoration. |
Wednesday, March 8, 2023 5:24PM - 5:36PM |
Q30.00013: What Sets the Magic Angle in Twisted Bi-Layer Graphene? Jose P Rodriguez We study the energy spectrum of bi-layer graphene at commensurate twist angles within the tight-binding description. We start with the smallest possible number of Moire reciprocal lattice vectors in the Brillouin zone of a single graphene sheet given by the prime numbers p = 7, 19, and 37. It is pointed out that the characteristic polynomial for the energy spectrum is governed by the cyclic group Zp, which is a simple group. The chiral limit is taken, where inter-sheet hopping between A sites only and between B sites only of the two honeycomb lattices is turned off. The dispersion in momentum of the remaining hopping matrix elements between the A sites in one honeycomb lattice and the B sites in the other honeycomb lattice is neglected, and it is replaced by an effective constant matrix element, w1. This approximation is valid in the low-energy limit, at small Moire Brillouin zones. We find numerically that flat low-energy bands appear at a magic effective matrix element w1*. The magic effective matrix element w1* for A/B inter-sheet hopping is thereby determined per commensurate twist angle θp. Comparison of these results with experimentally determined magic angles in twisted bi-layer graphene will be made. |
Wednesday, March 8, 2023 5:36PM - 5:48PM |
Q30.00014: Quantum quench dynamics in quantum impurity models using the auxiliary field approach Emmanuel L Bogacz, Andrew K Mitchell We study the transient dynamics of the interacting Anderson impurity model after a quantum quench. Specifically, we use the auxiliary field approach to calculate the time-dependence of the real-frequency impurity spectral function due to a sudden change in the impurity level energy or interaction strength. The auxiliary field approach [1] was recently introduced in the context of equilibrium dynamical mean field theory for the Hubbard model, and involves mapping the exact interaction self-energy to an effective non-interacting auxiliary system living in an enlarged Hilbert space. Here we generalize the method to a nonequilibrium setting which, although approximate, provides physical insights and qualitatively correct results at low computational cost. The structure of the auxiliary field is determined exactly from the equilibrium self-energy for the pre- and post-quench Hamiltonians (obtained here using the numerical renormalization group). The quench in the physical system is then assumed to correspond to a quench in the auxiliary field configuration, and the effect on the impurity dynamics is found using nonequilibrium Green's function methods. An immediate implication of the mapping is a light-cone effect, which means that low-energy spectral features take longer to relax than high-energy features. We discuss the possible consequences of this for quenching across the Mott transition in the Hubbard model, where nonequilibrium quasistationary states emerge at intermediate timescales. |
Wednesday, March 8, 2023 5:48PM - 6:00PM |
Q30.00015: Occupation-resolved conductance as a test for Kondo correlations in the mixed valence regime of few-electron quantum dots Johann Drayne, Tim J Child, Silvia Lüscher, Saeed Fallahi, Geoffrey C Gardner, Michael J Manfra, Yaakov Kleeorin, Yigal Meir, Joshua Folk We present a comparison between conductance measurements close to strongly-coupled Coulomb blockade peaks in a lithographically-defined quantum dot (QD), simultaneous charge sensing measurements of the QD occupation, and numerical renormalization group (NRG) simulations. |
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