Bad metallic transport in a cold atom Fermi-Hubbard system

TL;DR

This study investigates charge transport in a strongly interacting Fermi-Hubbard system using ultracold atoms, revealing bad metallic behavior characterized by linear temperature-dependent resistivity exceeding the Mott-Ioffe-Regel limit.

Contribution

It introduces a novel experimental method to measure charge diffusion and resistivity in ultracold atom systems, providing insights into bad metal phenomena in a clean quantum setting.

Findings

Charge diffusion constant measured via density relaxation.

Resistivity shows linear temperature dependence.

Resistivity exceeds the Mott-Ioffe-Regel limit.

Abstract

Charge transport is a revealing probe of the quantum properties of materials. Strong interactions can blur charge carriers resulting in a poorly understood "quantum soup". Here we study the conductivity of the Fermi-Hubbard model, a testing ground for strong interaction physics, in a clean quantum system - ultracold $^6$Li in a 2D optical lattice. We determine the charge diffusion constant in our system by measuring the relaxation of an imposed density modulation and modeling its decay hydrodynamically. The diffusion constant is converted to a resistivity, which exhibits a linear temperature dependence and exceeds the Mott-Ioffe-Regel limit, two characteristic signatures of a bad metal. The techniques we develop here may be applied to measurements of other transport quantities, including the optical conductivity and thermopower.