Viscosity and Thermal Relaxation for a resonantly interacting Fermi gas

TL;DR

This paper calculates how medium effects influence viscosity and thermal relaxation in a resonantly interacting Fermi gas, revealing significant enhancements near the superfluid transition temperature, especially at unitarity.

Contribution

It introduces a many-body scattering matrix that includes medium effects, providing new insights into relaxation rates near the superfluid transition in Fermi gases.

Findings

Relaxation rates increase significantly near T_c due to medium effects.

In the unitarity limit, relaxation rates nearly tenfold compared to no medium effects.

Trapped gases show about three times higher relaxation rates due to density inhomogeneity.

Abstract

The viscous and thermal relaxation rates of an interacting fermion gas are calculated as functions of temperature and scattering length, using a many-body scattering matrix which incorporates medium effects due to Fermi blocking of intermediate states. These effects are demonstrated to be large close to the transition temperature $T_c$ to the superfluid state. For a homogeneous gas in the unitarity limit, the relaxation rates are increased by nearly an order of magnitude compared to their value obtained in the absence of medium effects due to the Cooper instability at $T_c$. For trapped gases the corresponding ratio is found to be about three due to the averaging over the inhomogeneous density distribution. The effect of superfluidity below $T_c$ is considered to leading order in the ratio between the energy gap and the transition temperature.