Bulletin of the American Physical Society
51st Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 65, Number 4
Monday–Friday, June 1–5, 2020; Portland, Oregon
Session N06: FOCUS: Transport and Bad Metals in Strongly-Correlated Fermi-Hubbard ModelsFocus Live
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Sponsoring Units: DCMP Chair: Annabelle Bohrdt, The Entrepreneurial University Room: E141-142 |
Thursday, June 4, 2020 10:30AM - 11:00AM Live |
N06.00001: Bad-metal relaxation dynamics in a Fermi lattice gas Invited Speaker: Brian DeMarco Electrical current in conventional metals is carried by electrons that retain their individual character. Bad metals, such as the normal state of some high-temperature superconductors, violate this scenario, and the complete picture for their behavior remains unresolved. I will describe transport measurements consistent with bad metal phenomena for $^{40}$K atoms trapped in an optical lattice. In this system described by the Hubbard model, we measure the transport lifetime for a spin-selective mass current excited by stimulated Raman transitions. We demonstrate incompatibility with weak-scattering theory and key characteristics of bad metals: anomalous resistivity scaling consistent with T-linear behavior, the onset of incoherent transport, and the approach to the Mott-Ioffe-Regel limit. I will also briefly discuss recent measurements of the influence of disorder on doublon decay in this system. [Preview Abstract] |
Thursday, June 4, 2020 11:00AM - 11:30AM Live |
N06.00002: Transport in Fermi Hubbard models: lessons from weak coupling Invited Speaker: Erich Mueller In the absence of phase transitions, all of the strong coupling phenomena in cold atom experiments are continuously connected to physics at weak coupling. I will report on quantum Boltzman equation calculations of resistivity in the Fermi Hubbard model. Here the only mechanism for momentum relaxation is Umklapp scattering -- where quantum coherent two-particle scattering deposits momentum into a perfect lattice. At temperatures large compared to the bandwidth the scattering rates are temperature independent but resistivity nonetheless grows linearly with temperature because of band-filling effects. At temperature small compared to the bandwidth the resistivity generically has the Fermi-liquid form, $\rho\propto T^2$. The temperature of the crossover from quadratic to linear behavior depends on the filling, vanishing at half-filling -- where the resistivity is approximately linear for all temperatures. I will also report on a simple, yet quantitatively accurate, Gutzwiller Ansatz based calculation of the compressibility. [Preview Abstract] |
Thursday, June 4, 2020 11:30AM - 11:42AM Live |
N06.00003: Angle-resolved photoemission spectroscopy (ARPES) for quantum gas microscopes Fabian Grusdt, Annabelle Bohrdt, Daniel Greif, Frank Pollmann, Michael Knap, Eugene Demler Quantum gas microscopy provides a new perspective on strongly correlated quantum matter, such as the doped Fermi-Hubbard model. To connect such quantum simulation platforms with traditional solid state experiments, for example on the high-$T_c$ cuprate superconductors, spectroscopic tools are required. In this talk, an experimental protocol is presented which allows to perform (the analogue of) angle-resolved photoemission spectroscopy in state-of-the-art quantum gas microscopes. Theoretical results for the $t-J$ model in one and two dimensions are presented for low doping. Our numerical studies can be explained theoretically by a microscopic parton picture, even on a quantitative level. The results presented in this talk pave the way, in the short term, towards spectroscopic studies of the pseudogap phase in the doped Hubbard model, and, in the long term, novel studies of exotic quantum spin liquids in optical lattices. [Preview Abstract] |
Thursday, June 4, 2020 11:42AM - 11:54AM Live |
N06.00004: Subdiffusion and heat transport in a tilted Fermi-Hubbard system Elmer Guardado-Sanchez, Benjamin M. Spar, Waseem S. Bakr Understanding the transport properties of strongly interacting quantum systems is of great interest. Recently, quantum microscopy has been used to study diffusive charge transport in a cold atom Fermi-Hubbard system [1], revealing a strange metal phase with T-linear resistivity. In this work, we use the same technique to study the late-time effective hydrodynamics of a Fermi-Hubbard system subject to an external linear potential (a ``tilt"). The tilt couples mass transport to local heating through energy conservation. Due to this coupling the system quickly heats up to near infinite temperature in the lowest band of the lattice. We study the high-temperature transport and thermalization in our system as a function of tilt strength and find that the associated decay time $\tau$ crosses over as the tilt strength is increased from characteristically diffusive to subdiffusive with $\tau\propto\lambda^4$. In order to explain the underlying physics and emphasize its universal nature we develop a hydrodynamic model that exhibits this crossover. For strong tilts, the subdiffusive transport rate is set by a thermal diffusivity, which we are thus able to measure as a function of tilt in this regime. [1] P. T. Brown et al, Science 363, 379-382 (2019) [Preview Abstract] |
Thursday, June 4, 2020 11:54AM - 12:06PM Live |
N06.00005: Bilayer Fermi-Hubbard systems via Quantum Gas Microscope Pimonpan Sompet, Joannis Koepsell, Sarah Hirthe, Dominik Bourgund, Guillaume Salomon, Jayadev Vijayan, Immanuel Bloch, Christian Gross Ultracold atoms in optical lattices offer a unique route for the quantum simulation of the Hubbard model. Quantum gas microscopy with a single-site resolution has enabled the study of the interplay between spin and charge in both one- and two-dimensional strongly correlated systems. Here, we report on the experimental study of the bilayer Fermi-Hubbard (BFH) systems where the phase diagram of the BFH model at half filling is explored. To realize the coupled-bilayer systems, we implement a fully-controllable bichromatic vertical superlattice in our $^{\mathrm{6}}$Li quantum gas microscope. We perform geometric charge pumping to increase the separation between the layers and therefore achieve the single-site resolution images of both layers. Furthermore, we integrate the Stern-Gerlach splitting and the bilayer readout techniques which allows for spin-resolved two-dimensional Fermi-Hubbard systems in larger sizes. [Preview Abstract] |
Thursday, June 4, 2020 12:06PM - 12:18PM Live |
N06.00006: Dynamics of a Hole Dopant in a Fermi Hubbard Antiferromagnet Muqing Xu, Geoffrey Ji, Martin Lebrat, Lev Kendrick, Christie Chiu, Markus Greiner Ultracold fermions in optical lattices have opened new perspectives in the study of strongly correlated systems and have been used to realize the Fermi Hubbard model, which is believed to exhibit many quantum phases and to capture the essential physics of cuprate high-temperature superconductivity. The site-resolved readout and manipulation offered by quantum gas microscopy allows detailed exploration of the interplay between charge and spin, which underlies much of the phenomena of the Fermi Hubbard model with doping. On this platform we study the dynamics upon releasing an initially pinned hole dopant. We first prepare a two-component ultracold fermi gas with Lithium-6 loaded into a 2-dimensional square optical lattice at half-filling, which exhibits strong antiferromagnetic correlations. We use a digital micromirror device to create a pinned hole dopant while loading the lattice potential. We then release the dopant by quenching off the pinning potential and probe its motion and how it interacts with and scrambles the spin environment. The microscopic dynamics of dopants may provide further insights into understanding the quantum phases in the doped Hubbard model. [Preview Abstract] |
Thursday, June 4, 2020 12:18PM - 12:30PM Live |
N06.00007: Antiferromagnetic nearest-neighbor spin correlations of SU($N$) alkaline-earth fermions in an optical lattice Eduardo Ibarra Garcia Padilla, Kaden R A Hazzard, Hao-Tian Wei, Richard T Scalettar, Shintaro Taie, Naoki Nishizawa, Yosuke Takasu, Yoshihito Kuno, Yoshiro Takahashi Recently, the Kyoto experiment has detected nearest-neighbor antiferromagnetic (AFM) spin-correlations in an SU(6) $^{173}$Yb Fermi gas loaded in 1D, 2D, and 3D optical lattices, which is well-described by the SU(6) Fermi Hubbard model. We have calculated the experimentally measured properties in these systems, utilizing two numerically-exact methods we have developed: exact diagonalization that utilizes the SU($N$) symmetry and a physically-motivated basis truncation, and a determinant Quantum Monte Carlo method. We find that the calculated and measured nearest-neighbor AFM correlations agree quantitatively with no fitting for all temperatures in 1D, and at temperatures where converged theoretical results can be obtained in 3D. In 3D, the lowest temperatures achieved by the experiments are substantially below those attainable in simulation, making these experiments an exemplary case of quantum simulation. In 1D, the lowest temperature reached is $k_BT/t = 0.069 \pm 0.046 \pm 0.026$, inferred from theory using the experimentally-measured magnetic correlations. Error bars come from an estimate of finite-size error and the experimental uncertainty on the correlations, respectively. This is the lowest temperature $k_BT/t$ ever reported for a Fermi gas in an optical lattice. [Preview Abstract] |
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