Itinerant Ferromagnetism in a polarized two-component Fermi gas

TL;DR

This paper investigates the conditions under which a strongly polarized two-component Fermi gas becomes unstable and transitions to an itinerant ferromagnetic state, emphasizing the role of repulsive polarons and interaction parameters.

Contribution

It provides a detailed phase diagram analysis for itinerant ferromagnetism in polarized Fermi gases, highlighting the impact of interaction range and mass imbalance on polaron lifetime.

Findings

Longer polaron lifetime with increased interaction range.

Enhanced polaron stability with higher mass imbalance.

Potential for experimental detection of ferromagnetic transition.

Abstract

We analyze when a repulsively interacting two-component Fermi gas becomes thermodynamically unstable against phase separation. We focus on the strongly polarised limit where the free energy of the homogeneous mixture can be calculated accurately in terms of well-defined quasiparticles, the repulsive polarons. Phase diagrams as a function of polarisation, temperature, mass imbalance, and repulsive polaron energy, as well as scattering length and range parameter are provided. We show that the lifetime of the repulsive polaron increases significantly with the interaction range and the mass of the minority atoms, raising the prospects of detecting the transition to the elusive itinerant ferromagnetic state with ultracold atoms.