Theory of the Normal/Superfluid interface in population imbalanced Fermi gases

TL;DR

This paper theoretically investigates the interface between superfluid and normal phases in polarized Fermi gases, analyzing surface energy, structure, and experimental implications, and finds discrepancies with experimental data suggesting new mechanisms are needed.

Contribution

It provides mean-field estimates of surface energy and domain wall structure in polarized Fermi gases, highlighting inconsistencies with experimental surface tension measurements.

Findings

Mean-field estimates of surface energy vary with temperature and scattering length.

Microscopic calculations do not match experimental surface tension magnitudes.

Suggests the need for novel mechanisms to explain experimental observations.

Abstract

We present a series of theoretical studies of the boundary between a superfluid and normal region in a partially polarized gas of strongly interacting fermions. We present mean-field estimates of the surface energy in this boundary as a function of temperature and scattering length. We discuss the structure of the domain wall, and use a previously introduced phenomonological model to study its influence on experimental observables. Our microscopic mean-field calculations are not consistent with the magnitude of the surface tension found from our phenomonological modelling of data from the Rice experiments. We conclude that one must search for novel mechanisms to explain the experiments.