Itinerant ferromagnetism in an interacting Fermi gas with mass imbalance

TL;DR

This paper investigates how mass imbalance in an ultra-cold Fermi gas influences the emergence and detection of itinerant ferromagnetism, revealing unique experimental signatures and suppression of loss processes.

Contribution

It introduces a formalism for ferromagnetism in mass-imbalanced gases, analyzing phase behavior, experimental signatures, and dynamic formation post-quench.

Findings

Mass imbalance modifies the Stoner criterion for ferromagnetism.

Unique experimental signatures arise from mass imbalance in trapped gases.

Mass imbalance suppresses three-body loss processes, aiding ferromagnetic state formation.

Abstract

We study the emergence of itinerant ferromagnetism in an ultra-cold atomic gas with a variable mass ratio between the up and down spin species. Mass imbalance breaks the SU(2) spin symmetry leading to a modified Stoner criterion. We first elucidate the phase behavior in both the grand canonical and canonical ensembles. Secondly, we apply the formalism to a harmonic trap to demonstrate how a mass imbalance delivers unique experimental signatures of ferromagnetism. These could help future experiments to better identify the putative ferromagnetic state. Furthermore, we highlight how a mass imbalance suppresses the three-body loss processes that handicap the formation of a ferromagnetic state. Finally, we study the time dependent formation of the ferromagnetic phase following a quench in the interaction strength.