Large Amplitude Dynamics of the Pairing Correlations in a Unitary Fermi Gas

TL;DR

This paper investigates large amplitude pairing field modes in a unitary Fermi gas, revealing slow, collective oscillations that couple with density modes and are distinct from traditional hydrodynamic excitations.

Contribution

It uncovers a new class of slow, large amplitude pairing modes in a unitary Fermi gas that cannot be described by simplified models like quantum hydrodynamics.

Findings

Modes are slow with frequencies below the pairing gap.

These modes couple with density oscillations in traps.

They can be excited by rapid changes in scattering length.

Abstract

A unitary Fermi gas has a surprisingly rich spectrum of large amplitude modes of the pairing field alone, which defies a description within a formalism involving only a reduced set of degrees of freedom, such as quantum hydrodynamics or a Landau-Ginzburg-like description. These modes are very slow, with oscillation frequencies well below the pairing gap, which makes their damping through quasiparticle excitations quite ineffective. In atomic traps these modes couple naturally with the density oscillations, and the corresponding oscillations of the atomic cloud are an example of a new type of collective mode in superfluid Fermi systems. They have lower frequencies than the compressional collective hydrodynamic oscillations, have a non-spherical momentum distribution, and could be excited by a quick time variation of the scattering length.