Polarized superfluidity in the attractive Hubbard model with population imbalance

TL;DR

This paper investigates a polarized superfluid phase in an attractive Fermi system on a lattice, revealing its stability, characteristics, and energetic stabilization mechanisms, with implications for understanding imbalanced superfluidity.

Contribution

It demonstrates the existence and stability of a polarized superfluid in the attractive Hubbard model with population imbalance, highlighting its energetic stabilization and resemblance to the Sarma phase.

Findings

Polarized superfluid is stable at low temperatures.

Momentum distribution resembles the Sarma phase with two Fermi surfaces.

Potential energy gain stabilizes the polarized superfluid.

Abstract

We study a two-component Fermi system with attractive interactions and different populations of the two species in a cubic lattice. For an intermediate coupling we find a uniformly polarized superfluid which is stable down to very low temperatures. The momentum distribution of this phase closely resembles that of the Sarma phase, characterized by two Fermi surfaces. This phase is shown to be stabilized by a potential energy gain, as in a BCS superfluid, in contrast to the unpolarized BEC which is stabilized by kinetic energy. We present general arguments suggesting that preformed pairs in the unpolarized superfluid favor the stabilization of a polarized superfluid phase.