Bad-metal relaxation dynamics in a Fermi lattice gas

W Xu,B Demarco,W R Mcgehee,W N Morong

doi:10.1038/s41467-019-09526-x

Abstract

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. Here, we report phenomena consistent with bad-metal behaviour in an optical-lattice Hubbard model by measuring the transport lifetime for a 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. Our work demonstrates a direct method for determining the transport lifetime, which is critical to theory but difficult to measure in materials, and exposes minimal ingredients for bad-metal behavior.

Highlights

Electrical current in conventional metals is carried by electrons that retain their individual character
In ultracold gas experiments with fermionic atoms, photoemission spectroscopy has been used to probe the spectral function in the Bose–Einstein condensate (BEC)–Bardeen–Cooper–Schrieffer (BCS) crossover for a trapped gas, and a failure of Fermi liquid theory was discovered[26]
We describe a method for measuring the decay rate of a mass current and inferring the analog of electrical resistivity for a two-component fermionic gas composed of 40K atoms trapped in a cubic optical lattice

Summary

Introduction

Electrical current in conventional metals is carried by electrons that retain their individual character. In ultracold gas experiments with fermionic atoms, photoemission spectroscopy has been used to probe the spectral function in the Bose–Einstein condensate (BEC)–Bardeen–Cooper–Schrieffer (BCS) crossover for a trapped gas, and a failure of Fermi liquid theory was discovered[26]. Transport measurements such as diffusion in a 2D lattice gas[27], shear viscosity in a unitary Fermi gas[28], and spin diffusion[29] have explored the effect of strong interactions on various relaxation processes. The analog of resistivity is inferred from the transport lifetime and the atomic density

Methods

Results

Conclusion