Superfluid (Amplitude) Fluctuations Above $T_c$ in a Unitary Fermi Gas

TL;DR

This paper investigates how superfluid fluctuations influence the spin diffusion properties of a strongly interacting Fermi gas near the superfluid transition temperature, providing theoretical insights aligned with experimental data.

Contribution

It introduces a method to compute spin diffusion lifetime considering superfluid fluctuations using Landau parameters and induced interaction models.

Findings

Superfluid fluctuations significantly affect spin diffusion near $T_c$.

Theoretical results match experimental measurements when including superfluid fluctuations.

Finite temperature corrections improve the accuracy of diffusion lifetime calculations.

Abstract

We study the transport properties of a Fermi gas with strong attractive interactions close to the unitary limit. In particular, we compute the spin diffusion lifetime of the Fermi gas due to superfluid fluctuations above the BCS transition temperature $T_c$. To calculate the spin diffusion lifetime we need the scattering amplitudes. The scattering amplitudes are dominated by the superfluid fluctuations at temperatures just above $T_c$. The normal scattering amplitudes are calculated from the Landau parameters. These Landau parameters are obtained from the local version of the induced interaction model for computing Landau parameters. We also calculate the leading order finite temperature correction to the diffusion lifetime. A calculation of the spin diffusion coefficient is presented in the end. Upon choosing a proper value of $F_0^a$, we are able to present a good match between the theoretical result and the experimental measurement which indicates the presence of the superfluid fluctuations near $T_c$.