Spin-dipole mode in a trapped Fermi gas near unitarity

TL;DR

This paper theoretically studies the temperature-dependent spin-dipole oscillation in a strongly interacting Fermi gas near unitarity, revealing how pairing correlations influence collective modes both below and above the superfluid transition.

Contribution

It combines diagrammatic strong-coupling theory with local density approximation and sum rule approach to analyze spin-dipole frequencies near unitarity, highlighting the role of pairing correlations.

Findings

Spin-dipole frequency is enhanced in the superfluid state due to Cooper pairing.

Enhancement of spin-dipole frequency occurs even above the superfluid transition temperature.

The frequency exactly matches the trap frequency in a non-interacting Fermi gas.

Abstract

We theoretically investigate the spin-dipole oscillation of a strongly interacting Fermi gas in a harmonic trap. By using a combined diagrammatic strong-coupling theory with a local density approximation and a sum rule approach, we clarify the temperature dependence of the spin-dipole frequency near the unitarity, which is deeply related to the spin susceptibility, as well as pairing correlations. While the spin-dipole frequency exactly coincides with the trap frequency in a non-interacting Fermi gas, it is shown to remarkably be enhanced in the superfluid state, because of the suppression of the spin degree of freedom due to the spin-singlet Cooper-pair formation. In strongly interacting Fermi gases, this enhancement occurs even above the superfluid phase transition temperature, due to the strong pairing correlations.