Heavy-Light Fermion Mixtures at Unitarity

TL;DR

This paper uses Quantum Monte Carlo methods to study fermion pairing in a 6Li-40K mixture at unitarity, revealing nearly independent ground-state energies from mass ratio and phase separation behaviors.

Contribution

It provides new insights into the energy spectra and phase separation of heavy-light fermion mixtures at unitarity, especially regarding polarization and mass ratio effects.

Findings

Ground-state energy nearly independent of mass ratio

Polarized superfluid close to phase-separated mixture energy

Predicted phase separation in harmonic traps with three regions

Abstract

We investigate fermion pairing in the unitary regime for a mass ratio corresponding to a 6Li-40K mixture using Quantum Monte Carlo methods. The ground-state energy and the average light and heavy particle excitation spectrum for the unpolarized superfluid state are nearly independent of the mass ratio. In the majority light system, the polarized superfluid is close to the energy of a phase separated mixture of nearly fully polarized normal and unpolarized superfluid. For a majority of heavy particles, we find an energy minimum for a normal state with a ratio of ~ 3:1 heavy to light particles. A slight increase in attraction to kF*a ~ 2.5 yields a ground state energy of nearly zero for this ratio. A cold unpolarized system in a harmonic trap at unitarity should phase separate into three regions, with a shell of unpolarized superfluid in the middle.