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 M44: Theories of Exotic MetalsLive
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Sponsoring Units: DCMP Chair: Inti Sodemann, Max Planck Institute for the Physics of Complex Systems |
Wednesday, March 17, 2021 11:30AM - 11:42AM Live |
M44.00001: Simultaneous signatures of quantum spin liquid and broken symmetry in the Heisenberg spin-1/2 pyrochlore lattice Nikita Astrakhantsev, Tom Westerhout, Apoorv Tiwari, Kenny Jing Hui Choo, Ao Chen, Mark Fischer, Giuseppe Carleo, Titus Neupert The antiferromagnetic spin-1/2 pyrochlore has been discussed as a quantum spin liquid (QSL) candidate. To study the ground state properties and identify phase transitions to adjacent ordered phases, we employ two variational approaches, many-variable Monte Carlo and Neural Quantum States. Validating our results against exact diagonalization on a 32-spin cluster, we expand to large-scale lattices up to 256 spins. We find that the magnetic correlations show pronounced features of the $k =0$ ordered phase upon inclusion of next-to-nearest-neighbor interactions and sharply vanish in the vicinity of the putative QSL, accompanied by an entanglement spectrum degeneracy and reduced susceptibility to twisted boundary conditions expected from a QSL. However, the QSL region is considerably smaller than expected from weak-coupling studies. |
Wednesday, March 17, 2021 11:42AM - 11:54AM Live |
M44.00002: Parquet approach - the most fundamental diagrammatic method? Christian Eckhardt, Carsten Honerkamp, Patrick Kappl, Karsten Held, Anna Kauch In this talk we show that the parquet equation follows as natural and in fact completely analogous to well known diagrammatic equations like the Dyson or the Bethe-Salpeter equation. Furthermore, it has been shown that other well known methods like the GW approximation or the functional Renormalization Group (fRG) method emerge as ways to find an approximate solution to the parquet equation [1][2]. |
Wednesday, March 17, 2021 11:54AM - 12:06PM Live |
M44.00003: Composite Fermion Pairing in the ν=1/2+1/2 Bilayer at Large Layer Spacing Haoyun Deng, Luis E Mendoza, Nicholas Bonesteel We study interlayer pairing of composite fermions in the ν=1/2+1/2 quantum Hall bilayer. In the large layer spacing limit, ignoring disorder and for perfectly balanced wells, the interlayer pairing interaction mediated by the Chern-Simons gauge fields in the two layers is singular with both attractive (out-of-phase) and repulsive (in-phase) components. If only the singular attractive interaction is included the pairing gap obtained by solving the Eliashberg equations is proportional to the inverse of the layer spacing squared [1]. Analyzing these equations in the so-called local approximation [2] we find when the less singular repulsive interactions are included the energy gap is strongly suppressed, but still falls off as inverse layer spacing squared, consistent with recent RG analysis [3]. The (in some cases analytic) local approximation solutions are then used as a starting point to iterate the full Eliashberg equations to assess the validity of the approximation in this limit. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M44.00004: Breakdown of Emergent Lifshitz Symmetry in Holographic Matter with Harris-Marginal Disorder Koushik Ganesan, Andrew Lucas We revisit the theory of strongly correlated quantum matter perturbed by Harris-marginal random-field disorder, using the simplest holographic model. We argue that for weak disorder, the ground state of the theory is not Lifshitz invariant with a non-trivial disorder-dependent dynamical exponent, as previously found. Instead, below a non-perturbatively small energy scale, we predict infrared physics becomes independent of the disorder strength. |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M44.00005: Tightening the Lieb-Robinson bound in locally-interacting systems Zhiyuan Wang, Kaden Hazzard In a recent work [1] we have shown that the finite-size error of numerical simulations of many-body quantum dynamics can be bounded using Lieb-Robinson bounds. However, while quantitative accuracy of the LR bounds is crucial for this application and others, previous LR bounds are usually extremely loose. In this talk we present a method [2] that dramatically and qualitatively improves LR bounds in systems with finite-range interactions. In prototypical models such as spin-1/2 Ising and Fermi-Hubbard models, our method improves the LR velocity by an order of magnitude with typical model parameters. More prominently, in systems with a large local Hilbert space dimension D, our method gives a LR velocity that grows much slower than previous bounds as D becomes large. For example, in the large-spin limits of the Heisenberg model and Wen's quantum rotor model and the large-number-of-orbitals limit of Hubbard models, our method gives a finite LR speed while all previous bounds diverge. |
Wednesday, March 17, 2021 12:30PM - 12:42PM Live |
M44.00006: Hall coefficient of the t-J model Ilia Khait, Assa Auerbach DC transport coefficients of most strongly interacting Hamiltonians demand insurmountable computational challenges, e.g. large system sizes, long real-time evolution, and poorly controlled analytic continuation of quantum Monte Carlo data. In contrast, it was shown that continued fractions expansions and the use of Hall-type resistivities, require only computations of equilbrium averages. |
Wednesday, March 17, 2021 12:42PM - 12:54PM Live |
M44.00007: nonlinear response in strongly-correlated electron systems Yoshihiro Michishita, Robert Peters Nonlinear responses in condensed matter are intensively studied today. While the nonlinear responses in noninteracting models have been explored widely, the effect of strong correlations on the nonlinear response is still poorly understood, even though it has been suggested that correlations can enhance the nonlinear response.[1-3] |
Wednesday, March 17, 2021 12:54PM - 1:06PM Live |
M44.00008: Finite and Infinite Matrix Product States \\for Gutzwiller Projected Mean-Field Wavefunctions Gabriel Petrica, Bo-Xiao Zhang, Garnet Chan, Bryan Clark Matrix product states (MPS) and `dressed' ground states of quadratic mean fields (e.g. Gutzwiller projected Slater Determinants) are both important classes of variational wave-functions. This latter class has played important roles in understanding superconductivity and quantum spin-liquids. We present a novel method to obtain both the finite and infinite MPS (iMPS) representation of the ground state of an arbitrary fermionic quadratic mean-field Hamiltonian, (which in the simplest case is a Slater determinant and in the most general case is a Pfaffian). We also show how to represent products of such states (e.g. determinants times Pfaffians). From this representation one can project to single occupancy and evaluate the entanglement spectra after Gutzwiller projection. Additionaly, we develop an approach to orthogonalize degenerate iMPS to find all the states in the degenerate ground-state manifold. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M44.00009: Mean field solution of the quantum Coulomb glass Izabella Lovas, Annamaria Kiss, Catalin Pascu Moca, Gergely Zarand We study a mean field model for the Coulomb glass emerging from the interplay of strong interactions and disorder, by considering spinless fermions on the Bethe lattice in the limit of infinite coordination number. We combine quantum Monte-Carlo simulations with self-consistent diagrammatic perturbation theory to show that strong interactions induce a metallic Coulomb glass phase with a pseudogap structure at the Fermi energy. Quantum and thermal fluctuations both melt this glass and lead to a disordered quantum liquid phase. We obtain the complete phase diagram of the model, and characterize its dynamical properties in the replica symmetric liquid phase, as well as in the glassy phase in the presence of full replica symmetry breaking. The spectral function displays an Efros-Shklovskii pseudogap upon decreasing temperatures, but the density of states remains finite at the Fermi energy due to residual quantum fluctuations. Our results bear relevance to the metallic glass phase observed in Si inversion layers. |
Wednesday, March 17, 2021 1:18PM - 1:30PM Live |
M44.00010: Exact analytic solution of the infinite-dimensional extended Falicov-Kimball model: the phase diagram and thermodynamic properties Konrad Kapcia, Romuald Lemanski, Jakub Krawczyk, Marcin J. Zygmunt The Falicov-Kimball model [1] is a simplified version of the Hubbard model, where only electrons with, e.g., spin down, are itinerant and the other are localized. We discuss results for the extended Falicov-Kimball model at half-filling on the Bethe lattice in the large-dimension limit derived within the dynamical mean field theory formalism [2-3]. On-site U and intersite V density-density interactions between particles occupying neighboring sites are included in the Hamiltonian [2-5]. We determined the exact phase diagrams of the model both in the ground state [2] and at finite temperatures [3]. Using analytical formulas and having calculated the temperature dependent density of states we studied thermodynamic properties of the system starting from its free energy. We compared the results with those obtained within the standard Hartree-Fock approach [4,5]. |
Wednesday, March 17, 2021 1:30PM - 1:42PM Live |
M44.00011: Competition of Spinon Fermi Surface and Heavy Fermi Liquids states from the Periodic Anderson to the Hubbard model Chuan Chen, Inti A Sodemann, Patrick A Lee We study a model of correlated electrons coupled by tunnelling to a layer of itinerant electrons, which interpolates from a frustrated limit favorable to spin liquid states to a Kondo-lattice limit favorable to interlayer coherent heavy metallic states. Employing a slave rotor mean-field, we obtain a phase diagram and describe two regimes where the spin liquid state is destroyed by weak interlayer tunnelling, (i) the Kondo limit where the correlated electrons can be viewed as localized spin moments and (ii) near the Mott metal-insulator-transition where the spinon fermi surface transitions continuously into a Fermi liquid. We study the LDOS spectra of the correlated layer in the heavy Fermi liquid phase and describe the temperature dependence of its width arising from interactions and disorder effects. Comparison of theoretical results and recent experiments of the candidate spin liquid 1T-TaSe2 residing on metallic 1H-TaSe2 suggests that this system is either close to the localized Kondo limit, or in an intermediate coupling regime where the Kondo coupling and the Heisenberg exchange interaction are comparable, posing a challenge to the interpretation of this material as a candidate spin liquid. |
Wednesday, March 17, 2021 1:42PM - 1:54PM Live |
M44.00012: Fluctuation diagnostic of the nodal/antinodal dichotomy in the Hubbard model at weak coupling: a parquet dual fermion approach Friedrich Krien, Alexander I. Lichtenstein, Georg Rohringer We apply a dual fermion parquet scheme to the half-filled Hubbard model on a square lattice at small interaction. Our results establish that in this regime nonlocal vertex corrections play an important role in the formation of the pseudogap. Namely, in comparison to the simpler ladder approximation, these additional vertex corrections included in the parquet equations enhance the coupling of spin fluctuations with the quasiparticles. The pseudogap thus opens already |
Wednesday, March 17, 2021 1:54PM - 2:06PM Live |
M44.00013: Effects of three-body correlations on nonlinear current noise through an N-level Anderson impurity: NRG and large N studies Yoshimichi Teratani, Akira Oguri, Rui Sakano We study nonlinear transport through an N-level Anderson impurity with finite Coulomb interactions U at low bias voltages eV, using a Fermi-liquid theory which has recently been extended to arbitrary cases of electron fillings Nd [1,2]. The nonlinear current and noise up to order of (eV)3 are determined not only by phase shifts and charge and spin static susceptibilities but also three-body correlations between impurity electrons. We calculate these parameters up to N=8 by two methods: numerical renormalization group(NRG) and 1/(N-1) expansion[3]. The latter one is a large N theory which keeps (N-1)U constant. For strong interactions U, NRG results show that the three-body contributions can be described by a single parameter over a range of 1≤Nd≤N-1 [4,5]. We also find that the three-body correlations significantly affect the noise, especially near Nd=1 and Nd=N-1. Furthermore, the results of two methods agree well with each other already at N=8 for weak interactions. |
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