Phase diagram of a cold polarized Fermi gas

TL;DR

This paper maps out the phase diagram of a cold polarized Fermi gas, identifying four main phases and special critical points, and provides a universal effective theory near the splitting point.

Contribution

It introduces a comprehensive phase diagram for polarized Fermi gases, including new phases and critical points, with an effective field theory for the splitting point.

Findings

Identification of four main phases: superfluid, normal, gapless superfluid, and modulated.

Existence of a Lifshitz point and a splitting point with universal physics.

Subregions with one and two Fermi surfaces within phases.

Abstract

We propose a phase diagram for a cold polarized atomic Fermi gas with zero-range interaction. We identify four main phases in the plane of density and polarization: the superfluid phase, the normal phase, the gapless superfluid phase, and the modulated phase. We argue that there exists a Lifshitz point at the junction of the normal, the gapless superfluid, and the modulated phases, and a splitting point where the superfluid, the gapless superfluid, and the modulated phases meet. We show that the physics near the splitting point is universal and derive an effective field theory describing it. We also show that subregions with one and two Fermi surfaces exist within the normal and the gapless superfluid phases.