Single-particle excitations and the order parameter for a trapped superfluid Fermi gas

TL;DR

This paper investigates how the superfluid phase transition affects single-particle excitations in a trapped Fermi gas, revealing in-gap states and energy shifts that signal the transition.

Contribution

It demonstrates the impact of superfluidity on excitation spectra and proposes using these features to detect the phase transition in trapped Fermi gases.

Findings

Presence of in-gap excitations localized at the outer gas regions

Eigenenergies shift and lose simple harmonic relations below transition

Density oscillations change markedly across the superfluid transition

Abstract

We reveal a strong influence of a superfluid phase transition on the character of single-particle excitations of a trapped neutral-atom Fermi gas. Below the transition temperature the presence of a spatially inhomogeneous order parameter (gap) shifts up the excitation eigenenergies and leads to the appearance of in-gap excitations localized in the outer part of the gas sample. The eigenenergies become sensitive to the gas temperature and are no longer multiples of the trap frequencies. These features should manifest themselves in a strong change of the density oscillations induced by modulations of the trap frequencies and can be used for identifying the superfluid phase transition.