Spin Transport in Cold Fermi gases: A Pseudogap Interpretation of Spin Diffusion Experiments at Unitarity

TL;DR

This paper offers a pseudogap interpretation of spin diffusion experiments in ultracold unitary Fermi gases, explaining the temperature dependence of spin diffusivity and susceptibility within a non-Fermi liquid framework.

Contribution

It provides a theoretical explanation for experimental spin transport data using a pseudogap model, challenging the Fermi liquid assumption in low-temperature regimes.

Findings

Spin diffusivity decreases significantly at low temperatures.

Spin susceptibility measurements are consistent with a Fermi liquid when protocols are reconsidered.

Pseudogap effects can explain deviations from Fermi liquid behavior in spin transport.

Abstract

We address recent spin transport experiments in ultracold unitary Fermi gases. We provide a theoretical understanding for how the measured temperature dependence of the spin diffusivity at low $T$ can disagree with the expected behavior of a Fermi liquid (FL) while the spin susceptiblity(following the experimental protocols) is consistent with a Fermi liquid picture. We show that the experimental protocols for extracting $\chi_s$ are based on a FL presumption; relaxing this leads to consistency within (but not proof of) a pseudogap-based approach. Our tranport calculations yield insight into the measured strong suppression of the spin diffusion constant at lower $T$.