Spin drag in an ultracold Fermi gas on the verge of a ferromagnetic instability

TL;DR

This paper investigates how spin drag and spin diffusion behave near a ferromagnetic transition in ultracold Fermi gases, providing insights into experimental detection of ferromagnetic correlations.

Contribution

It introduces the analysis of spin drag relaxation and diffusion near the ferromagnetic critical point in ultracold Fermi gases, linking theoretical predictions to experimental observables.

Findings

Spin drag relaxation rate is strongly enhanced near the ferromagnetic transition.

Temperature dependence of the spin diffusion constant is characterized.

Spin dipole mode damping can serve as a precursor signal for ferromagnetic transition.

Abstract

Recent experiments [Jo et al., Science 325, 1521 (2009)] have presented evidence of ferromagnetic correlations in a two-component ultracold Fermi gas with strong repulsive interactions. Motivated by these experiments we consider spin drag, i.e., frictional drag due to scattering of particles with opposite spin, in such systems. We show that when the ferromagnetic state is approached from the normal side, the spin drag relaxation rate is strongly enhanced near the critical point. We also determine the temperature dependence of the spin diffusion constant. In a trapped gas the spin drag relaxation rate determines the damping of the spin dipole mode, which therefore provides a precursor signal of the ferromagnetic phase transition that may be used to experimentally determine the proximity to the ferromagnetic phase.