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 P21: Precision Many-Body Physics III: Gauge Fields, Topology, and FractionalizationFocus Live
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Sponsoring Units: DCOMP DAMOP DCMP Chair: Boris Svistunov, University of Massachusetts Amherst |
Wednesday, March 17, 2021 3:00PM - 3:36PM Live |
P21.00001: Particle transmutations in flat-band lattices: bosons to fermions, fermions to composite fermions. Invited Speaker: Saurabh Maiti Understanding new quantum states and exotic quasiparticles can often be facilitated by approaching the problem in a different basis. One such example, amongst many, is viewing hard core bosons as fermions coupled to a special gauge-field (called the Chern-Simons gauge field). The non-Maxwellian nature of this gauge field introduces new challenges in treating such a problem. However, progress has been made by treating the problem via various mean-field schemes. The most remarkable one, perhaps, is its application to fractional quantum hall states. In this talk, we will draw our attention to the consequences of one particular scheme that is designed to be applicable for various interesting 2D lattices. We will see how this scheme leads to a particular flux distribution that provides a natural description of the system in the parameter space where a chiral spin-liquid is stabilized for bosons residing in either a Honeycomb lattice or a Kagome lattice. We will view these results in light of other numerical works in the literature. Interestingly, we will also see that when the same scheme is applied to fermions in a lattice, subject to an external magnetic field, we can make interesting predictions related to the composite fermion state: in particular the theory suggests that Graphene with next nearest neighbor hopping at the half-filling condition should be a doped Haldane-Chern insulator of composite fermions. |
Wednesday, March 17, 2021 3:36PM - 3:48PM Live |
P21.00002: Isolation of Flat Band Jun Hyung Bae, Tigran Sedrakyan, Saurabh Maiti Flat band systems are becoming popular due to special properties. For instance, the strong correlation of electrons leads to realization of unconventional superconductivity [1]. Typically, such bands are only approximately flat and are engineered by fine tuning Vanderwaal’s structures. Here we consider Kagome and Lieb lattices with perfectly flat bands. However, at some points in the Brillouin zone the bands superimpose leading to degeneracies. It has been shown that the degeneracy can be lifted when time-reversal symmetry (TRS) is broken [2]. In this presentation, we explore further means to lift the degeneracy while preserving the flat band. We show that the flatness is robust under certain changes to the lattice and that breaking TRS is not sufficient to isolate the flat band. Instead, we show that modulating the flux based on Chern-Simons field as outlined in [3] successfully gaps out the band. |
Wednesday, March 17, 2021 3:48PM - 4:00PM Live |
P21.00003: Optical lattice platform for the SYK model Chenan Wei, Tigran Sedrakyan The Sachdev-Ye-Kitaev (SYK) model and its modifications have recently drawn broad theoretical interests due to their possibility to understand the non-Fermi liquid properties, maximally chaotic behavior, and holographic duality. A viable experimental realization of the SYK model is an important task that allows testing the basic understanding of the SYK physics going beyond the saddle point approximation and the conformally invariant solution. We show that the SYK Hamiltonian emerges from a system of spinless itinerant fermionic atoms in an optical Kagome lattice with disorders on random sites. We discuss the regimes supporting non-dispersive flat band spectra in a Kagome lattice. Random interaction between non-dispersive fermions is induced due to randomly distributed immobile impurities in the optical lattice that impede the presence of itinerant fermions at their locations. We show that the proposed setup represents a maximally chaotic system by checking that the distribution of eigenenergies satisfying the Wigner-Dyson ensemble. We discuss that the velocity distribution of the released fermions can be a sensitive probe of the spectral density while the averaged many-body Loschmidt echo scheme can measure two-point out-of-time-ordered correlation functions of the SYK system. |
Wednesday, March 17, 2021 4:00PM - 4:12PM Live |
P21.00004: Fock space localization in the Sachdev-Ye-Kitaev model Felipe Monteiro, Tobias Micklitz, Masaki Tezuka, Alexander Altland We study the physics of many body localization in the Majorana Sachdev-Ye-Kitaev (SYK) model perturbed by a one-body Hamiltonian. Specifically, we consider the statistics of many body wave functions and spectra as the strength of the one-body term is ramped up from an ergodic phase into a (Fock space) Anderson localized phase. Our results are obtained from an effective low energy theory, derived from the microscopic model by matrix integral techniques standard in the theory of disordered electronic systems. The analytical results produced by this formalism are compared to exact diagonalization for systems containing up to 30 Majorana fermions. The statistics of many body spectra and wave functions, and the indications of the localization transition are in quantitative agreement with numerics. We believe that this is the first many body system where a localization transition is observed in parameter free agreement with first principle analytical calculations. |
Wednesday, March 17, 2021 4:12PM - 4:24PM Live |
P21.00005: Anyonic vortex states of 3D interacting Bose systems Tigran Sedrakyan We formulate and study a generalization of the Chern-Simons transformation in interacting Bose systems to three-dimensional space (3D). The method combines ordinary Chern-Simons (CS) transformation on a 2D plane and Jordan-Wigner fermionization along the orthogonal arbitrary vortex line. This transformation defines the anyonic properties of vortexes. The transformation yields an action for the emergent matter fields coupled to a gauge field, the generalization of Chern-Simons action to 4D, which reproduces CS transformation at the level of the equations of motion. The obtained action contains metrics on a transversal to vortices planes with varying z-coordinates connected each with other by area-preserving diffeomorphisms. The action has the same structure as for 2d integrable models of classical statistical mechanics understood in terms of quantum gauge theory in four dimensions recently formulated in K. Costello, arXiv:1303.2632. We define the corresponding to our action 2D R-matrix and investigate its topological properties. We apply the obtained results to three-dimensional interacting Bose systems with an infinitely degenerate single-particle dispersion. We argue that these systems may exhibit an absence of condensation and stabilize ground states with anyonic vortices. |
Wednesday, March 17, 2021 4:24PM - 4:36PM Live |
P21.00006: Topological edge plasmons in graphene's viscous Hall fluid Wenbo Sun, Todd Van Mechelen, Ashwin Boddeti, Adrian Tepole, Hadiseh Alaeian, Zubin Jacob Graphene's viscous hall fluid is the first candidate for a non-local topological electromagnetic phase of matter. Here, the gap closes due to the viscous edge plasmons. This 2D topological viscous Hall insulator is characterized by an optical N invariant fundamentally different from the Chern insulator and quantum spin Hall insulator. It can support a unidirectional topological edge mode that is stable under various boundary conditions with different slip lengths and immune to back-scattering at edge defects. Here, we propose an ultra-subwavelength topological circulator (three-port non-reciprocal device) for THz region based on the unidirectional edge mode. The behavior of the circulator is studied by simulating a time-dependent linearized Navier-Stokes equation describing hall viscosity in fluid coupled to the electromagnetic field. We demonstrate the circulation behaviour of topological edge modes and the difference from traditional magnetoplasmons. Our work opens practical applications of graphene's viscous Hall fluid and simultaneously provides an experimental platform for studying topological hydrodynamics of light. |
Wednesday, March 17, 2021 4:36PM - 4:48PM Live |
P21.00007: Realizing a symmetry-protected topological phase in the antiferromagnetic spin-1/2 Hubbard ladder Sarah Hirthe, Pimonpan Sompet, Dominik Bourgund, Thomas Chalopin, Joannis Koepsell, Petar Bojović, Guillaume Salomon, Julian Bibo, Frank Pollmann, Timon Alexander Hilker, Christian Gross, Immanuel Felix Bloch The spin-1 Haldane chain is the paradigmatic example of symmetry protected topological (SPT) phases, which are characterized by non-local quantities and edge states. Here we report on the experimental realization of such a phase using ultracold fermions in optical lattices. Site-resolved potential shaping allows us to create a tailored spin-1/2 ladder geometry needed to explore the topologically nontrivial spin-1 phase. Harnessing the full spin and density resolution of our Fermi-gas microscope, we detect a finite non-local string correlator in the bulk and localized spin-1/2 states at the edges. We confirm the robustness of the state by tuning the ratio of the leg to rung coupling of the ladder. We finally go beyond the spin model and explore the effect of charge fluctuations on the SPT phase in the general Hubbard regime. |
Wednesday, March 17, 2021 4:48PM - 5:00PM Live |
P21.00008: Using multiple quantum coherences to diagnose equilibrium quantum phase transitions via out-of-time-ordered correlators without time reversal Sean Muleady, Robert J Lewis-Swan, Ana Maria Rey Quantum information science has recently motivated a theoretical push to characterize the critical region of a quantum phase transition (QPT) via information-theoretic quantities such as entanglement or coherence measures. At the same time, there has been a growing focus on the dynamics of quantum information and non-equilibrium systems due to improvements in atomic, molecular, and optical experiments. Here, we propose a new dynamical method to connect equilibrium QPTs and quantum coherence via out-of-time-ordered correlators (OTOCs) [1]. Using paradigmatic examples of QPTs, we show that an abrupt change in coherence and entanglement of the ground state across a QPT is observable in the spectrum of multiple quantum coherences, which are a special type of OTOC. We also develop a robust protocol to obtain the relevant OTOCs using quasi-adiabatic ramps through the ground state phase diagram, allowing for the detection of OTOCs without the need for time reversal of coherent dynamics, and making our protocol applicable for a broad range of current experiments in trapped ions and optical tweezer arrays. |
Wednesday, March 17, 2021 5:00PM - 5:12PM Live |
P21.00009: Multicritical deconfined quantum-criticality and Lifshitz point of a helical valence-bond phase Bowen Zhao, Jun Takahashi, Anders Sandvik In this talk, we will discuss two deformations of S = 1/2 square-lattice J-Q model, which hosts deconfined quantum phase transition between antiferromagnetic and dimerized (valence-bond solid) ground states [1]. In the first case, we introduce a term projecting staggered local singlets, which preserves all symmetries of the square lattice. The second case is a modulation of the J terms forming alternating “staircases” of strong and weak couplings, but still preserves the four-fold degeneracy of the columnar valence bond solid states. |
Wednesday, March 17, 2021 5:12PM - 5:24PM Live |
P21.00010: Quantum criticality in Heisenberg chains and ladders with long range antiferromagnetic interactions Luhang Yang, Phillip Weinberg, Adrian Feiguin In order to circumvent the Mermin-Wagner theorem and realize true spontaneous symmetry breaking in 1D and quasi-1D spin systems, we include RKKY-like long-range antiferromagnetic (AFM) interactions to effectively increase their dimensionality. For a critical value of the exponent in the long-range term, both Heisenberg chains and ladders exhibit a second order phase transition from a disordered to a spontaneously symmetry broken Néel phase. We study the spectral function of both models across the transition with the time-dependent DMRG method. In chains, deconfined spinons form gapless coherent bound states (magnons) and push the two spinon continuum to higher energies, while in ladders we observe a transition from well-defined gapless magnons to gapped triplons accompanied by a coherent amplitude mode. The dynamic critical exponent for the transition on ladders is found to be z=1, raising the possibility of deconfined criticality in this model. We complement our results with linear spin-wave and bond-operator calculations. |
Wednesday, March 17, 2021 5:24PM - 5:36PM Live |
P21.00011: Quantum magnet with a helical bond order adjacent to deconfined quantum criticality Jun Takahashi, Bowen Zhao, Anders Wilhelm Sandvik We have numerically discovered that a perturbation preserving the four-fold degeneracy of the VBS order in the JQ model, a 2+1D quantum magnet, creates an intermediate helical phase between the Néel and VBS phases [1]. By weakening the perturbation, the phase shrinks to a deconfined quantum critical (DQC) point [2]. Reconsidering the conventional DQC point as a multicritical point may explain previously observed irregular scalings in DQC [3]. |
Wednesday, March 17, 2021 5:36PM - 5:48PM On Demand |
P21.00012: Gapless quantum spin liquid and global phase diagram of the spin-1/2 J1-J2 square antiferromagnetic Heisenberg model Wen-Yuan Liu, Shoushu Gong, Yu-Bin Li, Didier Poilblanc, Wei-Qiang Chen, Zhengcheng Gu We use the state-of-the-art tensor network state method, specifically, the finite projected entangled pair state (PEPS) algorithm , to simulate the global phase diagram of spin-1/2 J1-J2 Heisenberg model on square lattices up to 24 × 24. We provide very solid evidences to show that the nature of the intermediate nonmagnetic phase is a gapless quantum spin liquid (QSL), whose spin-spin and dimer-dimer correlations both decay with a power law behavior. There also exists a valence-bond solid (VBS) phase in a very narrow region 0.56 ≤ J2/J1 ≤ 0.61 before the system enters the well known collinear antiferromagnetic phase. We stress that our work gives rise to the first solid PEPS results beyond the well established density matrix renormalization group (DMRG) through one-to-one direct benchmark for small system sizes. Thus our numerical evidences explicitly demonstrate the huge power of PEPS for solving long-standing 2D quantum many-body problems. The physical nature of the discovered gapless QSL and potential experimental implications are also addressed. (see arXiv:1908.09359, and arXiv:2009.01821) |
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