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 W30: Strongly Correlated Systems, Including Quantum Fluids and Solids XX |
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Sponsoring Units: DCMP Chair: Marc Vila Tusell, UC Berkeley and LBNL Room: Room 222/223 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W30.00001: Anomalous hydrodynamics with triangular point group in 2+1 dimensions Jinkang Guo We present a theory of hydrodynamics for a vector U(1) charge in 2+1 dimensions, whose rotational symmetry is broken to the point group of an equilateral triangle. We show that it is possible for this U(1) to have a chiral anomaly. The hydrodynamic consequence of this anomaly is the introduction of a ballistic contribution to the dispersion relation for the hydrodynamic modes. We simulate classical Markov chains and find compelling numerical evidence for the anomalous hydrodynamic universality class. Generalizations of our theory to other symmetry groups are also discussed. |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W30.00002: Quasiparticle lifetimes in two-dimensional Fermi liquids Johannes Hofmann, Ulf Gran With recent experimental advances in the creation of ultraclean two-dimensional materials and the observation of interaction-dominated electron transport, there is now a renewed interest in the seemingly well-understood topic of interacting Fermi liquids. In particular, it has been proposed that two-dimensional Fermi liquids admit two distinct and vastly separate characteristic lifetimes: While even-parity perturbations of the Fermi surface decay with the standard Fermi-liquid quadratic temperature scaling, odd-parity perturbations are predicted to decay much more slowly. This raises the tantalizing prospect of a novel Fermi liquid transport regime in which odd modes are collisionless but even modes are collision-dominated (i.e., hydrodynamic). We confirm this picture by developing a systematic basis expansion for the linearized Fermi-liquid collision integral valid at all temperatures, which not only provides a comprehensive description of the degenerate low-temperature regime but also encompass the high-temperature expansion of a classical gas. We compute the eigenvalues of the linearized collision integral, which set the quasiparticle decay rates, for the first 20 angular harmonics of the quasiparticle perturbation down to ultralow temperatures T/T_F = 10^{-5} and establish that odd-parity excitations cross over from a diffusive quadratic scaling at low temperatures to a new subdiffusive scaling with quartic temperature dependence at ultralow temperatures. Our work demonstrates that the crossover temperature to this new transport regime is a sizeable fraction of the Fermi temperatures and thus experimentally accessible. Moreover, the formalism we have developed can be used for general solutions of the Fermi liquid transport equations. |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W30.00003: Current noise of hydrodynamic electrons Aaron Hui A resistor at finite temperature produces white noise fluctuations of the current called Johnson-Nyquist noise. Measuring the amplitude of this noise provides a powerful primary thermometry technique to access the electron temperature at the nanoscale. In practical situations, one needs to generalize the Johnson-Nyquist theorem to handle spatially inhomogenous temperature profiles. Recent work provided such a generalization for ohmic devices obeying the Wiedemann-Franz law, and showed that Joule heating leads to a geometry-independent increase in Johnson noise. However, there has been great recent interest in strongly-interacting hydrodynamic electron systems which do not admit a local conductivity nor obey the Wiedemann-Franz law. Such systems provide unusual sensitivity for Johnson noise thermometry, but so far there is no theory to describe the current noise they produce. Here we consider low-frequency Johnson noise in the hydrodynamic setting for a rectangular geometry. Unlike in the ohmic setting, we find that the Johnson noise is no longer geometry-independent due to non-local viscous gradients. Nonetheless, ignoring the geometric correction only leads to an error of at most 40% as compared to naively using the ohmic result. |
Thursday, March 9, 2023 3:36PM - 3:48PM Author not Attending |
W30.00004: Dynamical multicritical front behaviour in an integrable quantum walk model Durganandini Pillarishetty We consider an integrable quantum walk model on a one-dimensional lattice with finite range hopping. Starting from a spatially inhomogeneous initial state, we show the emergence of a generalized hydrodynamic description in the large space-time limit by studying the time dependence of various observables of interest like the cumulative probability distribution, cumulative currents, full counting statistics, cumulants, entanglement entropy, etc, using a combination of the analytic method of stationary phase approximation and exact numerics. We show the existence of a global ”quasi-stationary state” which can be described in terms of the local density of quasi-particle excitations satisfying Euler type of hydrodynamic equations. The global quasi-stationary state is characterized by an infinite set of conservation laws. Furthermore, we show that there is anomalous scaling behaviour in the vicinity of the extremal fronts which can be described in terms of higher-order hydrodynamic equations. Thus, we find that while the observables show global scaling behaviour in the bulk, they exhibit anomalous subdiffusive scaling behaviour with multicritical exponents near extremal fronts. We point out interesting connections of the model with multicritical random matrix models and fermions in nonharmonic traps. We also connect the study to that of domain wall dynamics in spin chain systems with finite-range spin exchange interactions. |
Thursday, March 9, 2023 3:48PM - 4:00PM |
W30.00005: Coupled Goldstone Modes in Supersolids Milan Rakic, Derek K Lee, Andrew Ho Supersolids are quantum phases of matter that exhibit both superfluid and crystal-like properties and have experienced renewed interest due to recent experiments on graphene substrates[1] and dipolar BEC gases[2]. In this talk we present a homogenisation technique on a Gross-Pitaevskii model with a non-local interaction term and calculate elastic constants, inertial fraction and speeds of sound for a general supersolid of arbitrary interaction potential and dimension. We verify our results numerically and extend the discussion by developing a technique to apply this formalism to other systems of interest. We discuss also the application of a Bogoliubov fluctuation technique and compare results between the two formalisms. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W30.00006: Coulomb drag of viscous electron fluids: drag viscosity and negative drag conductivity Thomas L Schmidt, Eddwi H Hasdeo, Edvin G Idrisov We show that Coulomb drag in hydrodynamic bilayer systems leads to additional viscosity terms in the hydrodynamic equations, i.e., the drag and drag-Hall viscosities, besides the well-known kinematic and Hall viscosities. These new viscosity terms arise from a change of the stress tensor due to the interlayer Coulomb interactions. All four viscosity terms are tunable by varying the applied magnetic field and the electron densities in the two layers. At certain ratios between the electron densities in the two layers, the drag viscosity dramatically changes the longitudinal transport resulting in a negative drag conductivity. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W30.00007: Benchmarking Computational Methods for Hydrodynamics of Noisy Quantum Chains Stuart N Thomas, Christopher D White, Brayden A Ware, Jay D Sau In ergodic quantum spin chains, locally conserved quantities such as energy or particle number evolve according to hydrodynamic equations as they relax to equilibrium. Qualitatively the hydrodynamics is typically diffusive; however, quantitatively predicting the diffusion constant is generally challenging. We investigate the complexity and accuracy of computational techniques to compute diffusion constants and the approach to hydrodynamics using tensor network time-evolution of operators [1]. Density matrix truncations [2] greatly improve the convergence of such simulations, resulting in more precise estimates of the diffusion constant than previously achieved. The predictions and computational cost of the simulations are compared with computations using Krylov methods and the universal operator growth hypothesis [3]. We also use these methods to simulate hydrodynamics in spin chains with depolarizing noise, which is unavoidably present in experimentally accessible quantum systems. The noisy dynamics is well-described by a diffusion equation with an added slow decay of the conserved quantities and a noise-modified diffusion constant, and can be simulated with reduced computational complexity due to the destruction of long-range entanglement. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W30.00008: Anomalous Structural Phase Transition in Ferromagnetic SrCoO2.875 Amani S Jayakody The concept of electronic phase separation explains several unusual magnetic and electronic properties of doped perovskite oxides such as cuprates, manganites, and cobaltites. Strontium cobalt oxide with varying oxygen concentration (SrCoO3-y, 0 < y < 0.125) is one of the systems which shows magnetic phase separation for intermediate oxygen values. The end points are SrCoO2.875 which is ferromagnetic with Tc=220 K and SrCoO3 which is also ferromagnetic but with Tc=280K. Samples with intermediate values of oxygen concentration show two phase magnetic behavior between these values, but a single average structure as determined by diffraction. We undertook high resolution x-ray powder diffraction measurements to better understand the underlying structure. SrCoO3 remains in the simple cubic perovskite structure from 10–300 K. SrCoO2.875 has a much more complicated structure. At room temperature it is tetragonal with an expanded unit cell. Upon cooling, the structure appears to undergo a second order transition to a cubic phase. This is extremely unusual and the opposite of typical structural transitions which proceed to lower symmetry structures at lower temperatures. We present our structural studies of the phases identified. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W30.00009: The shared universality of charged black holes and the many many-body SYK model Jan Louw, Stefan Kehrein There are various reasons to believe that Sachdev-Ye-Kitaev (SYK) models are simple examples of condensed-matter/gravity dualities. Motivated by this, we discuss a novel thermodynamic connection between the charged many many-body SYK model and charged black holes. The first many refers to $q$-body interactions and treating $1/q$ as an expansion parameter. Taking $q o infty$ one then obtains the leading order corrections. By varying the chemical potential or temperature, the condensed-matter system undergoes a phase transition between maximally chaotic gaseous and liquid phases. A similar transition is seen in charged AdS black holes with a small and a large event horizon phase, both also being maximally chaotic. Analytically calculating the critical exponents, we find that these models also share a universality class. At lower temperatures, the liquid phase becomes integrable while the gaseous phase remains maximally chaotic. This is reminiscent of another gravitational instability—the Hawking-Page transition between a large black hole and free thermal radiation. This talk is based on arXiv: 2204.09629. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W30.00010: Unruh Effect and Takagi's Statistics Inversion in Strained Graphene Anshuman Bhardwaj, Daniel Sheehy We present a theoretical study of how a spatially-varying quasiparticle velocity in honeycomb lattices, achievable using strained graphene or in engineered cold-atom optical lattices that have a spatial dependence to the local tunneling amplitude, can yield the Rindler Hamiltonian embodying an observer accelerating in Minkowski spacetime. Within this setup, a sudden switch-on of the spatially-varying tunneling (or strain) yields a spontaneous production of electron-hole pairs, an analogue version of the Unruh effect characterized by the Unruh temperature. We discuss how this thermal behavior, along with Takagi's statistics inversion, can manifest themselves in photoemission and scanning tunneling microscopy experiments. We also calculate the average electronic conductivity and find that it grows linearly with frequency ω, vanishing in the DC limit (ω → 0). Finally, we find that the total system energy at zero environment temperature looks like Planck's blackbody result for photons due to the aforementioned statistics inversion, whereas for an initial thermally excited state of fermions, the total internal energy undergoes stimulated particle reduction. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W30.00011: Exceptional Symmetry of G2 in Spin-3/2 Fermion Systems Zhi-Qiang Gao, Congjun Wu As the smallest exceptional Lie group and the automorphism group of the non-associative algebra of octonions, G2 is often employed for describing exotic symmetry structures. We prove a G2 symmetry in a Hubbard-like model with spin-3/2 fermions in a bipartite lattice, which lies in the intersection of two SO(7) algebras connected by the structure constants of octonions and dual to each other. Depending on the representations of the order parameters, the G2 symmetry can be spontaneously broken into either an SU(3) one associated with Goldstone manifold S6, or into an SU(2) × U(1) with a Grassmannian Goldstone manifold. In the quantum disordered states, quantum fluctuations generate the effective SU(3) and SU(2) × U(1) gauge theories for low energy fermions, both of which are of interest in high energy physics. In (1+1) spacetime dimension, this model shows a triality relation among three different phases, which is inherited from the underlying SO(8) structure. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W30.00012: Imaginary boost deformation of integrable models Taozhi Guo, Ryota Nakai, Kohei Kawabata, Shinsei Ryu Some integrable models in 1+1 dimension preserve Lorentz symmetry. We treat the Lorentz boost operator as a generator and deform the Hamiltonian with an imaginary parameter. The complex energy spectrum of the boosted non-Hermitian Hamiltonian emerges from infinity. We compute the energy spectrums and winding numbers for the free Fermion model, XXZ model, and Calogero Sutherland model. Non-Hermitian skin effect is observed on single-particle and two-particle energy spectrums. We also discuss the relation between boost deformation and Lorentz transformation on lattice systems and transport properties generated by the boost deformation. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W30.00013: Krylov Spaces for Truncated Spectrum Methodologies Robert M Konik, Marton K Lajer We propose herein an extension of truncated spectrum methodologies (TSMs), a non-perturbative numerical approach able to elucidate the low energy properties of quantum field theories. TSMs, in their various flavors, involve a division of a computational Hilbert space, H, into two parts, one part, H1, that is `kept' for the numerical computations, and one part, H2, that is discarded or `truncated'. Even though H2 is discarded, TSMs will often try to incorporate the effects of H2 in some effective way. In these terms, we propose to keep the dimension of H1 small (even considering the extreme case of H1=1). We pair this choice of H1 with a Krylov subspace iterative approach able to take into account the effects of H2. This iterative approach can be taken to arbitrarily high order and so offers the ability to compute quantities to arbitrary precision. In many cases it also offers the advantage of not needing an explicit UV cutoff. To compute the matrix elements that arise in the Krylov iterations, we employ a Feynman diagrammatic representation that is then evaluated with Monte Carlo techniques. Each order of the Krylov iteration is variational and is guaranteed to improve upon the previous iteration. The first Krylov iteration is akin to the NLO approach of Elias-Miró et al. (PRD 96 6 065024, 2017).To demonstrate this approach, we focus on the 1+1d Φ4 model and compute the bulk energy and mass gaps in both the Ζ2-broken and unbroken sectors. We estimate the critical Φ4 coupling in the broken phase to be gc=0.269(2). |
Thursday, March 9, 2023 5:36PM - 5:48PM |
W30.00014: Topology shared between classical metamaterials and interacting superconductors Michael J Lawler, Po-Wei Lo, Chao-Ming Jian Supersymmetry has been studied at a linear level between normal modes of metamaterials described by rigidity matrices and non-interacting quantum Hamiltonians. Recently, insight into the behavior of nonlinear mechanical systems was found by defining topological indices via the Poincaré-Hopf index. It turns out, because of the mathematical similarity, this topological index shows a way to approach supersymmetric quantum theory from classical mechanics. Using this mathematical similarity, we establish a topological connection between isostatic mechanical metamaterials and supersymmetric quantum systems, such as certain electron-phonon problems in metals and superconductors. Specifically, we show that a topological invariant derived from the Poincaré-Hopf index of a classical metamaterial is exactly the same as the Witten index of the supersymmetric electron-phonon problem. Our result shows that (1) classical metamaterials can be used to study the topology of interacting quantum systems with aid of supersymmetry, and (2) with fine-tuning between anharmonicity of phonons and couplings among Majorana fermions and phonons, it is possible to realize such a supersymmetric quantum system that shares the same topology as classical mechanical systems. |
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