Fermi-Fermi Mixtures in the Strong Attraction Limit

TL;DR

This paper analyzes the phase diagrams of low density Fermi-Fermi mixtures with strong attraction, revealing stable non-uniform states and effects of trapping potentials, with implications for ultracold fermion experiments.

Contribution

It provides a detailed description of phase diagrams and stable states in Fermi-Fermi mixtures in the strong attraction limit, including effects of mass, population imbalance, and trapping potentials.

Findings

Identification of stable phase separation states.

Phase diagrams generated using exact scattering lengths.

Effects of trapping potential on density profiles.

Abstract

The phase diagrams of low density Fermi-Fermi mixtures with equal or unequal masses and equal or unequal populations are described at zero and finite temperatures in the strong attraction limit. In this limit, the Fermi-Fermi mixture can be described by a weakly interacting Bose-Fermi mixture, where the bosons correspond to Feshbach molecules and the fermions correspond to excess atoms. First, we discuss the three and four fermion scattering processes, and use the exact boson-fermion and boson-boson scattering lengths to generate the phase diagrams in terms of the underlying fermion-fermion scattering length. In three dimensions, in addition to the normal and uniform superfluid phases, we find two stable non-uniform states corresponding to (1) phase separation between pure unpaired (excess) and pure paired fermions (molecular bosons); and (2) phase separation between pure excess fermions and a mixture of excess fermions and molecular bosons. Lastly, we also discuss the effects of the trapping potential in the density profiles of condensed and non-condensed molecular bosons, and excess fermions at zero and finite temperatures, and discuss possible implications of our findings to experiments involving mixtures of ultracold fermions.