Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session F49: Precision Many-Body Physics II: Topology and Strong CorrelationsFocus Recordings Available
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Sponsoring Units: DCOMP DAMOP DCMP Chair: Ke Wang, University of Massachusetts, Amherst Room: McCormick Place W-471B |
Tuesday, March 15, 2022 8:00AM - 8:36AM |
F49.00001: Sounds and turbulence in a 2D Bose gas Invited Speaker: Zoran Hadzibabic I will discuss our recent experiments on driven box-trapped 2D Bose gases. We have observed first and second sound in this system, which is the first such observation in a Berezinskii-Kosterlitz-Thouless (BKT) superfluid. The measured speeds of the two sounds allow extraction of the superfluid density, which agrees with the expected universal jump at the critical point. I will also discuss our new results on strongly driven 2D gases in which a direct turbulent cascade emerges. |
Tuesday, March 15, 2022 8:36AM - 8:48AM |
F49.00002: Precision Many-Body Study of the BKT Transition and Temperature-Dependent Properties in the Two-Dimensional Fermi Gas Yuan-Yao He, Hao Shi, Shiwei Zhang We perform large-scale, numerically exact Quantum Monte Carlo [1] calculations on the two-dimensional interacting Fermi gas with a contact attraction. Reaching much larger lattice sizes and lower temperatures than previously possible, we determine systematically the finite-temperature phase diagram of the Berezinskii-Kosterlitz-Thouless (BKT) transitions for interaction strengths ranging from BCS to crossover to BEC regimes. The evolutions of the pairing wavefunctions and the fermion and Cooper pair momentum distributions with temperature are accurately characterized. In the crossover regime, we find that the contact has a non-monotonic temperature dependence, first increasing as temperature is lowered, and then showing a slight decline below the BKT transition temperature to approach the ground-state value [2] from above. We also compute the equation of state as a function of interaction strength for various temperatures. We expect that these results will serve as a useful guide for future experiments, and provide unbiased comparison and benchmark for the other analytical and computational studies. |
Tuesday, March 15, 2022 8:48AM - 9:00AM |
F49.00003: Precision thermodynamics of the strongly interacting cold atomic Fermi gas in two spatial dimensions Shasta Ramachandran, Scott Jensen, Yoram Alhassid The two-species Fermi gas in two spatial dimensions (2D) with an attractive short- range interaction undergoes at zero temperature a crossover from a Bardeen- Cooper-Schrieffer (BCS) condensate to a Bose-Einstein condensate (BEC) as a function of the scattering length. This system exhibits features that are unique to two dimensions, including the presence of a bound state for an arbitrarily weak attractive interaction and the Berezinskii-Kosterlitz-Thouless character of the phase transition to a superfluid below a critical temperature. Of particular interest is the strongly correlated regime which lies between the BCS and BEC limits. Using finite-temperature auxiliary-field quantum Monte Carlo (AFMC) calculations, performed on discrete lattices and extrapolated to the continuum limit, we investigate the thermodynamic behavior of the 2D system across the strongly interacting regime. In particular, we discuss the extent of a pseudogap regime, in which pairing correlations survive above the critical temperature for superfluidity. We also discuss the calculation of dynamical observables, such as the single-particle spectral function, through the use of numerical analytic continuation. |
Tuesday, March 15, 2022 9:00AM - 9:12AM |
F49.00004: Operationally Accessible Entanglement in the 1D Bose-Hubbard Model Emanuel Casiano-Diaz, Chris M Herdman, Adrian G Del Maestro Conserved quantities, such as the total particle number in a many-body system, may reduce the amount of entanglement that is operationally accessible as a resource for quantum information processing. This reduction can be quantified via the accessible or symmetry-resolved entanglement entropies, which take these conservation laws into account. In this talk, we present quantum Monte Carlo results for the Rényi generalized accessible entanglement in the ground state of the Bose-Hubbard model accross the superfluid-insulator quantum phase transition in one dimension. We move beyond previous exact diagonalization studies and present results for the scaling with respect to the size of the spatial biparition at the critical point and discuss the role of particle number fluctuations in reducing the entanglement. |
Tuesday, March 15, 2022 9:12AM - 9:24AM |
F49.00005: Sensitivity of Quantum Information Measures to Local Bosonic Occupation Restrictions Hatem N Barghathi, Adrian G Del Maestro Discrete lattice models play an essential role in the understanding of quantum phenomena, but their exact numerical solution is hindered by the exponentially growing size of the underlying Hilbert space. Such difficulty is more pronounced in the case of bosons due to the lack of any occupation restrictions as opposed to fermionic or even spin models. Thus, a widely adopted approximation in exact diagonalization as well as in the Density Matrix Renormalization Group is to restrict the bosonic occupation numbers to only a few bosons per lattice site. While the corresponding relative errors under this approximation in many observables including the energy or local particle number fluctuations could be negligible, we report that imposing such restrictions could have drastic effects on quantum information measures such as particle and accessible (symmetry resolved) entanglement entropies. We find that in these cases, the error scales with the system size and thus could rapidly exceed 100%, as demonstrated in the ground state of the Bose-Hubbard model. |
Tuesday, March 15, 2022 9:24AM - 9:36AM |
F49.00006: The three-state quantum Potts paramagnet protected by S_3 symmetry Tigran A Sedrakyan, Hrant Topchyan, Mkhitar Mirumyan, Shahane A Khachatryan, Tigran Hakobyan We report a realization of a three-state Potts paramagnet with gapless edge modes on a triangular lattice that is protected by Z_3 symmetry. We study various microscopic models for the gapless edge and discuss the corresponding conformal field theories and their central charges. These are the Z_3 analogs of free fermion XX model edge term obtained by Levin and Gu for the Z_2 Ising paramagnet. The obtained edge theories do not belong to the integrable set of Fateev-Zamolodchikov models, and neither coincide with the chiral Potts model. |
Tuesday, March 15, 2022 9:36AM - 9:48AM Withdrawn |
F49.00007: Emergent Kondo behavior from gauge fluctuations in spin liquids Rui Wang, Baigeng Wang, Y. X Zhao, yilin wang Kondo effect is a prominent quantum phenomenon describing the many-body screening of a local magnetic impurity. Here, we reveal a new type of non-magnetic Kondo behavior generated by gauge fluctuations in strongly-correlated baths. We show that a non-magnetic bond defect not only introduces the potential scattering but also locally enhances the gauge fluctuations. The local gauge fluctuations further mediate a pseudospin exchange interaction that produces an asymmetric Kondo fixed point in low-energy. The gauge-fluctuation-induced Kondo phenomena do not exhibit the characteristic resistivity behavior of conventional Kondo effect, but display a non-monotonous temperature dependence of thermal conductivity as well as an anisotropic pseudospin correlation. Moreover, with its origin from gauge fluctuations, the Kondo features can be regarded as promising indicators for identifying quantum spin liquids. Our work advances fundamental knowledge of novel Kondo phenomena in strongly-correlated systems, which have no counterparts in thermal baths within the single-particle description. |
Tuesday, March 15, 2022 9:48AM - 10:00AM |
F49.00008: The fate of spin-charge separation in the presence of long-range antiferromagnetism Luhang Yang, Phillip E Weinberg, Adrian E Feiguin We present a numerical study of competing orders in the 1D t-J model with long range RKKY-like staggered spin interactions. By circumventing the constraints imposed by Mermin-Wagner's theorem, this Hamiltonian can realize long-range Néel order at and near half-filling. Upon doping, interactions induce a confining potential that binds holons and spinons forming full fledged polaronic quasi-particles. We determine the full phase diagram as a function of the exchange and density using the density matrix renormalization group (DMRG) method. We show that pairing is disfavored and the AFM insulator and polaronic metal phase are separated by a range of densities with phase segregation, while spin-charge separation re-emerges at low densities. In addition, we calculate the photoemission spectrum of the model, showing the emergence of a coherent polaronic band splitting away from the holon-spinon continuum with a regime realizing hole pockets. |
Tuesday, March 15, 2022 10:00AM - 10:12AM |
F49.00009: Multipoint Correlation Functions: Spectral Representation and Numerical Evaluation Jan Von Delft, Fabian B Kugler, Seung-Sup B Lee One-particle (or two-point) correlation functions have a well-known Lehmann representation, revealing the relation between their real- and imaginary-frequency variants, and can be computed by several means. For two-particle (or four-point) functions, an analogous representation and non-perturbative numerical results were previously known for imaginary frequencies only, and results on the real-frequency axis largely remained elusive. Here, we present spectral representations for multipoint correlation functions for each of three widely-used formalisms: the zero-temperature, Matsubara, and Keldysh formalisms. The spectral representations separate information on the system's dynamics, encoded in universal partial spectral functions, from the correlators' analytical properties, encoded in formalism-dependent convolution kernels. Using a novel numerical renormalization group scheme, we compute results for the four-point vertex of the Anderson impurity model. Starting with the Matsubara formalism, our approach allows us to obtain results at arbitrarily low temperatures. Continuing with the Keldysh formalism, we consider the dynamical mean-field solution of the Hubbard model and discuss the rich real-frequency structure of the vertex in the metal-insulator coexistence regime. |
Tuesday, March 15, 2022 10:12AM - 10:24AM |
F49.00010: Unfolding the spectral function of SrMoO3 Alexander Hampel, Edoardo Cappelli, Cyrus E Dreyer, Anna Tamai, Felix Baumberger, Antoine Georges The electronic spectral function obtained from angular-resolved photoelectron spectroscopy (ARPES) often provides the most detailed picture of the electronic structure of a material that can be obtained experimentally. This can be directly compared with ab initio calculations, e.g., based on density functional theory plus dynamical mean field (DFT+DMFT). Here we showcase a high precision comparison between theory and experiment using the distorted perovskite oxide SrMoO3 as an example. First, the DMFT equations are solved directly on the real frequency axis with the Fork Tensor-Product States (FTPS) method. Then, the resulting spectral function is unfolded into the higher-symmetry cubic unit cell, showing that structural properties play a crucial role in correctly interpreting the ARPES spectra. Finally, the analysis of the spectral function is performed utilizing a newly developed WebApp: "FermiSee", which makes the analysis of spectral properties of Wannier-like Hamiltonians easily accessible. We demonstrate how this WebApp enables straightforward analysis of spectral properties of correlated models and realistic materials alike. For the case of SrMoO3, this analysis reveals no indications of plasmonic features at lower binding energies, resolving a long standing controversy between theory and experiment for this specific material. |
Tuesday, March 15, 2022 10:24AM - 10:36AM |
F49.00011: Quantum many-body scars from infinite temperature thermofield-double states in bilayer systems Julia S Wildeboer, Christopher M Langlett, Zhicheng Yang, Alexey V Gorshkov, Thomas Iadecola, Shenglong Xu Recently, a new class of quantum many-body scar (QMBS) states --called rainbow scars-- was introduced in arXiv:2107.03416. In this work, we explore a closely related construction of QMBS based on infinite-temperature thermofield-double (TFD) states, which we dub TFD scars. The construction naturally applies to bilayer systems, including both spatial bilayers (with two spatially separated layers) and ``internal'' bilayers where the two layers correspond to different internal degrees of freedom (e.g., electron spins). Like the rainbow scar states, the TFD scars exhibit extensive bipartite entanglement entropy between the two layers despite having a simple entanglement structure. We explicitly investigate several bilayer systems with different kinds of degrees of freedom, e.g. spins, bosons, fermions, and quantum dimers with constrained Hilbert spaces. Some of the examples we consider subsume previously known examples of quantum many-body scars, including the spin-1 XY model and the $\eta$-pairing states in Fermi-Hubbard-like models. Furthermore, the construction also leads to new examples of QMBS, including in Bose-Hubbard and quantum dimer models. Building on recent experimental advances, we discuss potential relations to systems that can be engineered in a laboratory setting. |
Tuesday, March 15, 2022 10:36AM - 10:48AM |
F49.00012: Equilibrium Spectral Functions from Finite-temperature Real-Time One-particle Green's Functions for Realistic Systems Thomas J Blommel, Emanuel C Gull Equilibrium spectral functions are of central importance in condensed matter physics, providing information about the states available to the electrons in a system. Real-frequency spectral functions are typically calculated by analytically continuing imaginary-time equilibrium Green's functions. In this work, we obtain finite-temperature real-time self-consistent Green's Functions within the second-order self-energy approximation by solving the equilibrium Kadanoff-Baym equations. We then obtain real-frequency spectral functions from the Fourier transform of this data. Results for molecular systems are discussed and compared to current state of the art calculations. |
Tuesday, March 15, 2022 10:48AM - 11:00AM |
F49.00013: Modeling polymer systems in the presence of non-trivial topological relations: a combined analytical-numerical approach Franco Ferrari The news that will be delivered in this talk is that field theories are back to the realm of polymer physics and may be effectively used in order to understand the statistical behavior of knotted and concatenated polymer rings in a melt or in solution. This is a good news because for a long time analytical models of polymer rings subjected to topological constraints have been considered as mathematically intractable. |
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