Mixtures of ultracold fermions with unequal masses

TL;DR

This paper explores the phase diagram and superfluid properties of two-species ultracold fermion mixtures with unequal masses, covering the BCS to BEC crossover, and discusses topological transitions, collective excitations, and trap effects.

Contribution

It provides a comprehensive analysis of superfluid phases, phase transitions, and collective modes in mass-imbalanced fermion mixtures across interaction regimes.

Findings

Identified normal and superfluid phases with topological transitions.

Derived Ginzburg-Landau equation near critical temperature.

Obtained collective excitation spectrum consistent with Bogoliubov theory.

Abstract

We analyze the phase diagram of superfluidity for two-species fermion mixtures from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensation (BEC) limit as a function of scattering parameter, population imbalance and mass anisotropy. We identify regions corresponding to normal, or uniform/non-uniform superfluid phases, and discuss topological quantum phase transitions in the BCS, unitarity and BEC limits. We derive the Ginzburg-Landau equation near the critical temperature, and show that it describes a dilute mixture of paired and unpaired fermions in the BEC limit. We also obtain the zero temperature low frequency and long wavelength collective excitation spectrum, and recover the Bogoliubov relation for weakly interacting dilute bosons in the BEC limit. Lastly, we discuss the effects of harmonic traps and the resulting density profiles in the BEC regime.