Anisotropic acoustics in dipolar Fermi gases

TL;DR

This paper investigates anisotropic acoustic modes in ultracold dipolar Fermi gases, revealing directional differences in sound speed and damping, and introduces shear waves as a method to measure anisotropic viscosity coefficients.

Contribution

It provides a theoretical analysis of anisotropic acoustic and shear modes in dipolar Fermi gases, proposing experimental techniques to measure viscosity anisotropies.

Findings

Longitudinal waves show anisotropic sound speed and damping.

Two types of shear waves are identified, with unique density and temperature modulations.

Shear modes can be used to measure viscosity anisotropies experimentally.

Abstract

We consider plane wave modes in ultracold, but not quantum degenerate, dipolar Fermi gases in the hydrodynamic limit. Longitudinal waves present anisotropies in both the speed of sound and their damping, and experience a small, undulatory effect in their flow velocity. Two distinct types of shear waves appear, a ``familiar" one, and another that is accompanied by nontrivial density and temperature modulations. We propose these shear modes as an experimental means to measure the viscosity coefficients, including their anisotropies.