Quadrupole oscillation in a dipolar Fermi gas: hydrodynamic vs collisionless regime

TL;DR

This paper investigates the surface quadrupole oscillation modes of a dipolar Fermi gas in different regimes, revealing how anisotropy and trap geometry influence frequencies and offering a tool to study phase transitions.

Contribution

It provides a detailed analysis of quadrupole oscillation frequencies in both hydrodynamic and collisionless regimes, considering dipolar interactions and trap geometry effects.

Findings

Hydrodynamic regime frequency slightly below √2ω_perp

Collisionless regime frequency varies around 2ω_perp depending on aspect ratio

Quadrupole oscillation frequency can indicate phase transitions and collisional regimes

Abstract

The surface quadrupole mode of an harmonically trapped dipolar Fermi gas is studied in both the hydrodynamic and collisionless regimes. The anisotropy and long range effects of the dipolar force as well as the role of the trapping geometry are explicitly investigated. In the hydrodynamic regime the frequency is always slightly smaller than the $\sqrt{2}\omega_\perp$ value holding for gases interacting with contact interactions. In the collisionless regime the frequency can be either pretty smaller or larger than the non-interacting value $2\omega_\perp$, depending on the cloud aspect ratio. Our results suggest that the frequency of the surface quadrupole oscillation can provide a useful test for studying, at very low temperatures, the transition between the normal and the superfluid phase and, in the normal phase at higher temperatures, the crossover between the collisional and collisionless regimes. The consequences of the anisotropy of the dipolar force on the virial theorem are also discussed.