Viscosity-entropy ratio of the unitary Fermi gas from zero-temperature elementary excitations

TL;DR

This paper models the low-temperature viscosity-entropy ratio of a unitary Fermi gas using zero-temperature excitation spectra, aligning qualitatively with experimental data and identifying a minimum ratio near T/T_F ≈ 0.27.

Contribution

It introduces a theoretical model based on zero-temperature excitations to predict the viscosity-entropy ratio in a unitary Fermi gas, matching experimental trends.

Findings

The viscosity-entropy ratio ta/s reaches a minimum of about 0.44 at T/T_F  0.27.

The theoretical model qualitatively agrees with experimental measurements.

The study provides insights into low-temperature transport properties of ultracold Fermi gases.

Abstract

We investigate the low-temperature behavior of the ratio between the shear viscosity \eta and the entropy density s in the unitary Fermi gas by using a model based on the zero-temperature spectra of both bosonic collective modes and fermonic single-particle excitations. Our theoretical curve of \eta/s as a function of the temperature T is in qualitative agreement with the experimental data of trapped ultracold 6Li atomic gases. We find the minimum value \eta/s \simeq 0.44 (in units of \hbar/k_B) at the temperature T/T_F \simeq 0.27, with T_F the Fermi temperature.