Itinerant Ferromagnetism in a Fermi Gas of Ultracold Atoms

TL;DR

This paper provides experimental evidence that a two-component ultracold Fermi gas can undergo a phase transition to itinerant ferromagnetism due to repulsive interactions, confirming a fundamental theoretical model.

Contribution

First experimental demonstration of itinerant ferromagnetism in a Fermi gas, validating the Stoner model without lattice or band structure.

Findings

Observation of non-monotonic behavior in lifetime, energy, and size with increasing repulsion

Evidence of a phase transition to a ferromagnetic state

Confirmation that delocalized fermions can exhibit ferromagnetism without a lattice

Abstract

Can a gas of spin-up and spin-down fermions become ferromagnetic due to repulsive interactions? This question which has not yet found a definitive theoretical answer was addressed in an experiment with an ultracold two-component Fermi gas. The observation of non-monotonic behavior of lifetime, kinetic energy, and size for increasing repulsive interactions provides strong evidence for a phase transition to a ferromagnetic state. It implies that itinerant ferromagnetism of delocalized fermions is possible without lattice and band structure and validates the most basic model for ferromagnetism introduced by Stoner.