Radial quadrupole and scissors modes in trapped Fermi gases across the BCS phase transition

TL;DR

This paper investigates the excitation spectra of radial quadrupole and scissors modes in ultracold Fermi gases across the BCS transition, revealing how their spectral features evolve with temperature and interaction strength.

Contribution

It introduces a transport theory framework that unifies superfluid and normal phase descriptions of collective modes in Fermi gases across the BCS transition.

Findings

Spectra show multiple peaks shifting from hydrodynamic to collisionless frequencies with temperature.

The theory explains the observed frequency jump of the radial quadrupole mode.

Spectral analysis aligns with recent experimental observations.

Abstract

The excitation spectra of the radial quadrupole and scissors modes of ultracold Fermi gases in elongated traps are studied across the BCS superfluid-normal phase transition in the framework of a transport theory for quasiparticles. In the limit of zero temperature, this theory reproduces the results of superfluid hydrodynamics, while in the opposite limit, above the critical temperature, it reduces to the collisionless Vlasov equation. In the intermediate temperature range, the excitation spectra have two or three broad peaks, respectively, which are roughly situated at hydrodynamic and collisionless frequencies, and whose strength is shifted from the hydrodynamic to the collisionless modes with increasing temperature. By fitting the time dependent quadrupole deformation with a damped oscillation of a single frequency, we can understand the "jump" of the frequency of the radial quadrupole mode as a function of interaction strength which has recently been reported by the Innsbruck group.