Collective Excitations of Trapped Imbalanced Fermion Gases

TL;DR

This paper theoretically investigates the collective excitations in trapped imbalanced fermion gases at unitarity, focusing on superfluid and normal shell interactions, and calculates mode frequencies under different conditions.

Contribution

It introduces a comprehensive model for boundary conditions and analyzes collective modes in both hydrodynamic and collisionless regimes.

Findings

Out-of-phase modes exist below trapping frequency in hydrodynamic normal shells.

Collisionless case shows monopole modes with potential damping of higher modes.

Mode frequencies depend on trap polarization and shell dynamics.

Abstract

We present a theoretical study of the collective excitations of a trapped imbalanced fermion gas at unitarity, when the system consists of a superfluid core and a normal outer shell. We formulate the relevant boundary conditions and treat the normal shell both hydrodynamically and collisionlessly. For an isotropic trap, we calculate the mode frequencies as a function of trap polarization. Out-of-phase modes with frequencies below the trapping frequency are obtained for the case of a hydrodynamic normal shell. For the collisionless case, we calculate the monopole mode frequencies, and find that all but the lowest mode may be damped.