Spin polarizability of a trapped superfluid Fermi gas

TL;DR

This paper calculates the spin polarizability of a trapped superfluid Fermi gas at unitarity, revealing that pair-breaking energy costs suppress linear magnetic responses and cause deviations from ideal gas behavior, with implications for different trapping conditions.

Contribution

It introduces a theoretical framework for understanding spin polarizability in superfluid Fermi gases, accounting for phase separation and pair-breaking effects at zero temperature.

Findings

Dipole magnetic polarizability vanishes in the linear limit.

Significant deviations from ideal gas behavior occur even for small displacements.

Magnetic behavior varies with different trapping frequencies for spin species.

Abstract

The polarization produced by the relative displacement of the potentials trapping two spin species of a dilute Fermi gas with $N_\ua=N_\da$ is calculated at unitarity by assuming phase separation between the superfluid and a spin polarized phase at zero temperature. Due to the energy cost associated with pair breaking, the dipole magnetic polarizability vanishes in the linear limit and exhibits important deviations from the ideal gas behaviour even for displacements of the order of the size of the atomic cloud. The magnetic behaviour in the presence of different trapping frequencies for the two spin species is also discussed.