Two-species fermion mixtures with population imbalance

TL;DR

This paper explores the phase diagram of two-species fermion mixtures with population imbalance, revealing asymmetric stability regions, topological phase transitions, and a Ginzburg-Landau description near critical temperature.

Contribution

It provides a comprehensive analysis of the phase diagram across BCS-BEC crossover, highlighting effects of mass imbalance and population imbalance on superfluid stability and phase transitions.

Findings

Asymmetric stability regions for superfluidity with lighter fermions in excess.

Identification of topological quantum phase transitions related to quasiparticle energies.

Derivation of Ginzburg-Landau equation describing a mixture of composite bosons and unpaired fermions.

Abstract

We analyze the phase diagram of uniform superfluidity for two-species fermion mixtures from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) limit as a function of the scattering parameter and population imbalance. We find at zero temperature that the phase diagram of population imbalance versus scattering parameter is asymmetric for unequal masses, having a larger stability region for uniform superfluidity when the lighter fermions are in excess. In addition, we find topological quantum phase transitions associated with the disappearance or appearance of momentum space regions of zero quasiparticle energies. Lastly, near the critical temperature, we derive the Ginzburg-Landau equation, and show that it describes a dilute mixture of composite bosons and unpaired fermions in the BEC limit.