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 L43: Quantum Fluids & SolidsLive
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Sponsoring Units: DCMP Chair: Brad Rubin, American Physical Society |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L43.00001: Electron-phonon hydrodynamics Xiaoyang Huang, Andrew Lucas We develop the theory of hydrodynamics of an isotropic Fermi liquid of electrons coupled to isotropic acoustic phonons, assuming that umklapp processes may be neglected. At low temperatures, the fluid is approximately Galilean invariant; at high temperatures, the fluid is nearly relativistic; at intermediate temperatures, there are seven additional temperature regimes with unconventional thermodynamic properties and hydrodynamic transport coefficients in a three-dimensional system. We predict qualitative signatures of electron-phonon fluids in incoherent transport coefficients, shear and Hall viscosity, and plasmon dispersion relations. Our theory may be relevant for numerous quantum materials where strong electron-phonon scattering has been proposed to underlie a hydrodynamic regime, including WTe2, WP2, and PtSn4. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L43.00002: Fermionic superfluidity in finite one-dimensional spin-imbalanced systems: A configuration-space Hartree-Fock-Bogoliubov approach Kelly Patton, Daniel E Sheehy Ground state Hartree-Fock-Bogoliubov (HFB) theory is applied to spin imbalanced one dimensional Fermi systems with short-range interactions that are spatially confined by either a harmonic or a hard-wall trapping potential. It has been hoped that such systems, which can be realized using ultracold atomic gases, would exhibit the long-sought-after Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) superfluid phase. The HFB energy is expressed in the single-particle basis of the non-interacting Hamiltonian. The ground-state-energy is then found via numerical minimization. In addition to allowing for arbitrary Cooper pairing, the HFB approach also fully accounts for the effects of both the inhomogeneous trapping potential and the mean-field Hartree potential. We show that the local superfluid order parameter displays an oscillating FFLO-like characteristic; although we do find an imprint of the FFLO state in the local densities, it is weak in the harmonic trap case. In contrast, in the hard-wall geometry, shows a strong signature of the spatial oscillations of the FFLO pairing amplitude reflected in the local densities; here the excess spins are strongly localized near regions where there is a node in the pairing amplitude, thus creating an unmistakeable crystalline modulation of the density. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Live |
L43.00003: Vortices and Fractons Darshil Doshi, Andrey Gromov We propose a novel mechanism for fractons with promising experimental availability. More concretely, we demonstrate that a system of vortices in an incompressible superfluid exhibits fractonic behavior; rooted in non-commutativity of the configuration space. This system exhibits conservation of dipole moment of vorticity as well as trace of quadrupole moment. We show an equivalence to Traceless Scalar Charge Theory; both analytically and through phenomenological comparison. The conservation laws persist in the collective field theory of many vortices. We show that behavior of the vortex system on curved surfaces agrees with the existing literature on fractons. This mechanism for fractonicity opens up a new paradigm of interesting extensions. We offer one such example that exhibits an even higher set of conservation laws. |
Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L43.00004: Fracton models with crystalline symmetries in two dimensions Tianyu He, Andrey Gromov We construct dipole conserving models invariant under crystalline symmetries. Excitations of these models are fractons. We further show how to gauge the dipole symmetries. Upon gauging we introduce gauge fields that transform under irreducible representations of discrete rotations. As a concrete example, we discuss a D4 symmetric model on a lattice, which can be coupled to a spin-2 gauge theory of point group C4. The known traceless scalar charge theory is a special continuum limit of our model. Discussions about charge mobility and Wilson strips are included. Next, we generalize our model to wallpaper groups p4mm (symmorphic) and p4gm (non-symmorphic). Where in p4gm (non-symmorphic) case we show that fields with two flavors are necessary to implement fractional translations. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L43.00005: Multi-component Solitons in Atomic Bose-Einstein Condensates Panayotis Kevrekidis In this talk, we will mention a number of recent developments on multi-component wave patterns in Bose-Einstein |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L43.00006: Variational and parquet-diagram calculations for neutron matter: S-wave pairing Eckhard Krotscheck, Jiawei Wang We apply parquet-diagram summation methods for the calculation of the superfluid gap in S-wave pairing in neutron matter for realistic nucleon-nucleon interactions such as the Argonne v6 and the Reid v6 potentials. It is shown that diagrammatic contributions that are outside the parquet class play an important role. These are, in variational theories, identified as so-called ``commutator contributions''. Moreover, using a particle-hole propagator appropriate for a superfluid system results in the suppression of the spin-channel contribution to the induced interaction. Applying these corrections to the pairing interaction, our results agree quite well with Quantum Monte Carlo data. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L43.00007: Observation of Wigner crystal of electrons in a monolayer semiconductor Tomasz Smolenski, Pavel Dolgirev, Clemens Kuhlenkamp, Alexander Popert, Yuya Shimazaki, Patrick Back, Martin Kroner, Kenji Watanabe, Takashi Taniguchi, Ilya Esterlis, Eugene Demler, Atac Imamoglu If the Coulomb repulsion between the electrons becomes significantly stronger than their kinetic energy, the itinerant electrons in the two-dimensional systems are expected to form a Wigner crystal (WC). Here we provide a direct evidence that the electrons at densities < 3×1011 cm-2 in a MoSe2 monolayer spontaneously break continuous translation symmetry and form a WC even at B = 0 [*]. This is revealed by our low-temperature (T = 80 mK) optical experiments that utilize a newly developed technique of detecting a charge order. This method is based on the observation of the exciton umklapp or, equivalently, Bragg scattering off the WC that gives rise to emergence of a new, umklapp peak in the optical excitation spectrum. By tracing the evolution of this peak with the magnetic field and electron density we determined the WC phase properties at fields up to B = 16 T. We provide a qualitative explanation of these findings with a tentative phase-diagram obtained from our Hartree-Fock calculations. Altogether, our results evidence that gate-controlled TMD monolayers allow for exploration of strongly-correlated electronic states in previously inaccessible regime where inter-electron interactions are much stronger than the kinetic energy. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L43.00008: Phases and collective modes of bosons in a triangular lattice at finite temperature: A cluster mean field study Manali Malakar, Sayak Ray, Subhasis Sinha, Dilip Angom Motivated by the realization of Bose-Einstein condensates (BEC) in non-cubic lattices, in this work we study the phases and collective excitation of bosons with nearest neighbor interaction in a triangular lattice at finite temperature, using mean field (MF) and cluster mean field (CMF) theory. We compute the finite temperature phase diagram both for hardcore and softcore bosons, as well as analyze the effect of correlation arising due to lattice frustration and interaction systematically using the CMF method. A semi-analytic estimate of the transition temperatures between different phases is derived within the framework of MF Landau theory, particularly for hardcore bosons. Apart from the usual phases such as density waves (DW) and superfluid (SF), we also characterize different supersolids (SS). These phases and their transitions at finite temperatures are identified from the collective modes. The low lying excitations, particularly Goldstone and Higgs modes of the supersolid can be detected in the ongoing cold atom experiments. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L43.00009: Beyond Ohm's law -- Bernoulli effect and streaming in electron hydrodynamics Aaron Hui, Vadim Oganesyan, Eun-Ah Kim Recent observations of non-local transport in ultraclean 2D materials raised the tantalizing possibility of accessing hydrodynamic correlated transport of many-electron state. However, it has been pointed out that non-local transport can also arise from impurity scattering rather than interaction. At the crux of the ambiguity is the focus on linear effects, i.e. Ohm's law, which cannot easily differentiate among different modes of transport. Here we propose experiments that can reveal rich hydrodynamic features in the system by tapping into the non-linearity of the Navier-Stokes equation. Three experiments we propose will each manifest unique phenomenon well-known in classical fluids: the Bernoulli effect, Eckart streaming, and Rayleigh streaming. Analysis of known parameters confirms that the proposed experiments are feasible and the hydrodynamic signatures are within reach of graphene-based devices. Experimental realization of any one of the three phenomena will provide a stepping stone to formulating and exploring the notions of nonlinear electron fluid dynamics with an eye to celebrated examples from classical non-laminar flows, e.g. pattern formation and turbulence. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L43.00010: Electric polarization as a nonquantized topological response and boundary Luttinger theorem Xueyang Song, Yin-Chen He, Ashvin Vishwanath, Chong Wang We develop a nonperturbative approach to the bulk polarization of crystalline electric insulators in d ≥ 1 dimensions. Formally, we define polarization via the response to background fluxes of both charge and lattice translation symmetries. In this approach, the bulk polarization is related to properties of magnetic monopoles under translation symmetries. Specifically, in 2d the monopole is a source of 2π-flux, and the polarization is determined by the crystal momentum of the 2π-flux. In 3d the polarization is determined by the projective representation of translation symmetries on Dirac monopoles. Our approach also leads to a concrete scheme to calculate polarization in 2d, which in principle can be applied even to strongly interacting systems. For open boundary condition, the bulk polarization leads to an altered ‘boundary’ Luttinger theorem (constraining the Fermi surface of surface states) and also to modified Lieb-Schultz-Mattis theorems on the boundary. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L43.00011: Semiclassical theory of finite temperature dynamics of the sine-Gordon model Marton Kormos, Dániel Vörös, Catalin Pascu Moca, Gergely Zarand We investigate the finite temperature dynamics of the sine-Gordon model by studying its dynamical correlation functions at low temperatures in the semiclassical approach. Going beyond previous analyses based on perfectly reflective or transmissive collision dynamics of the gapped solitonic excitations, we focus on the generic case when both transmissive and reflective scatterings are present. We argue that the universal behaviour of the correlation functions is qualitatively different from both special cases. In particular, the autocorrelation function decays in time neither exponentially nor as a power-law, but assumes a squeezed exponential form. Supporting our claim, we perform semiclassical Monte Carlo simulations utilizing the exact S-matrix of the model, and we construct an approximate analytic description based on the symmetric exclusion process. |
Wednesday, March 17, 2021 10:12AM - 10:24AM Live |
L43.00012: Crystal-to-Fracton Tensor Gauge Theory Dualities Zhengzheng Zhai, Michael Pretko, Leo R Radzihovsky
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Wednesday, March 17, 2021 10:24AM - 10:36AM Live |
L43.00013: Half-Quantum Vortices in the Superfluid Phases of $^3$He Confined in Nafen Robert Regan, Joshua J Wiman, James Sauls Based on a strong-coupling Ginzburg-Landau theory that accounts for the relative stability of the confined equal-spin pairing superfluid phases in $^3$He, we report theoretical calculations for the structure of half-quantum vortices (HQVs) in the confined phases of $^3$He. We predict the regions of stability for two different ground state vortex phases within these confined phases, and provide an identification of the topological defects order parameter, mass currents, and spin-polarization. We investigate a pair of polar HQVs that are stabilized in the polar phase, and a newly discovered pair of polar-distorted chiral HQVs in the polar-distorted chiral A phase. We lastly calculate the confined superfluid phase diagram in a magnetic field, $H = 0 - 370G {\bf{Ω}}$, and obtain excellent agreement with the experimentally reported phase transitions observed in the equal-spin pairing phases of $^3$He. |
Wednesday, March 17, 2021 10:36AM - 10:48AM Live |
L43.00014: An SO(5) Topological Superfluid William Holdhusen, Sergio Lerma-Hernández, Gerardo Ortiz, Jorge Dukelsky The magnetic superfluid phases of Helium-3 have been identified with triplet pairing states, but as of yet no unifying theory exists to describe transitions between these states. In this work, we derive an extension of the exactly-solvable SO(5) Richardson-Gaudin model with p-wave pairing and Heisenberg interactions. This model contains topological and trivial superfluid phases, with a quartet ground state occurring at the critical SO(5)-symmetric point separating these quantum fluids. Under the influence of an external magnetic field, the ground state of this Hamiltonian retains its superfluid character with no pair breaking, exhibiting a series of transitions into a fully spin-polarized triplet state. A symmetry analysis of the ground state wavefunction is revealing. |
Wednesday, March 17, 2021 10:48AM - 11:00AM Live |
L43.00015: Fermionic propagator path integral Monte Carlo of the uniform electron gas and hydrogen plasma at warm-dense matter conditions Alexey Filinov, Michael Bonitz A significant progress has been achieved in studying exchange and correlation effects in fermionic systems using a fully anti-symmetrised density matrix propagator [1]. Ab initio results for the uniform electron gas (UEG) has been reported in a broad range of densities and temperatures~[2]. Here we extend the ideas of Refs.~[1,2] and formulate a new scheme for the grand canonical ensemble. Our simulations confirm the results of Ref.~[2] for UEG and lead to new predictions including pressure, chemical potential, pair correlation and momentum distribution functions. Furthermore, we also simulate hydrogen plasma down to temperatures 15 000 K including the transion to a molecular phase. The isotherms for the pressure and the internal energy are compared with FN-PIMC~[3] and hydrogen EOS based on DFT-MD [4]. Our results allow us to conclude on the accuracy of the fixed-node approximation depending on the degeneracy parameter. |
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