Effects of a Fluctuating Interface between a Superfluid and a Polarized Fermi Gas

TL;DR

This paper investigates how quantum and thermal fluctuations at the interface between a superfluid and a polarized Fermi gas influence observable properties, providing theoretical predictions consistent with experimental data.

Contribution

It introduces a theory describing interface fluctuations that explain partially polarized regimes and density profiles in trapped Fermi gases.

Findings

Interface fluctuations can induce partially polarized regions even without a bulk phase.

Predicted spatial profiles match experimental measurements from MIT and Rice groups.

Large fluctuations can cause density imbalances at the trap center.

Abstract

Motivated by recent experiments in trapped Fermi gas with spin population imbalance, we discuss the effects of the quantum and thermal fluctuations of the interface between a fully paired superfluid core and a fully polarized Fermi gas. We demonstrate that even if there is no true partially polarized thermodynamic phase in bulk, the interface fluctuation can give rise to a partially polarized transition regime in trap. Our theory yields a definite prediction for the functional forms of the spatial profile of spin polarization and pairing gap, and we show that the spin-resolved density profiles measured by both the MIT and Rice groups obey this function form. We also show that sufficient large fluctuation will lead to a visibly unequal density even at the center of the cloud. We hope this picture can shed lights on the controversial discrepancies in recent experiments.