BEC-BCS crossover in "magnetized" Feshbach-resonantly paired superfluids

TL;DR

This paper explores the phase diagram of a magnetized fermionic superfluid near a Feshbach resonance, revealing various phases including BCS-BEC crossover, phase separation, and Fulde-Ferrell-Larkin-Ovchinnikov states, depending on detuning and magnetization.

Contribution

It provides a detailed mapping of the phase diagram for magnetized Feshbach-resonant superfluids, highlighting the stability regions of different phases and the emergence of exotic states.

Findings

Normal magnetized Fermi gas stable above a critical population difference.

Existence of a coexistence phase with superfluid and normal components.

Identification of a finite-momentum FFLO phase in the BCS regime.

Abstract

We map out the detuning-magnetization phase diagram for a ``magnetized'' (unequal number of atoms in two pairing hyperfine states) gas of fermionic atoms interacting via an s-wave Feshbach resonance (FR). For large positive FR detuning a normal magnetized Fermi gas is stable above an exponentially small value of the population difference. Below this critical value the phase diagram is dominated by coexistence of a magnetized normal gas and a singlet paired superfluid with the latter exhibiting a BCS-Bose Einstein condensate crossover with reduced detuning. On the BCS side of strongly overlapping Cooper pairs, a sliver of finite-momentum paired Fulde-Ferrell-Larkin-Ovchinnikov magnetized phase intervenes between the phase separated and normal states. In contrast, for large negative detuning a uniform, polarized superfluid, that is a coherent mixture of singlet Bose-Einstein-condensed molecules and fully magnetized single-species Fermi-sea, is a stable ground state.