Spin Drag in Ultracold Fermi Mixtures with Repulsive Interactions

TL;DR

This paper investigates how spin-drag relaxation rates behave in ultracold Fermi gases across different dimensions, revealing temperature-dependent vanishing rates and enhancement near ferromagnetic transitions due to spin fluctuations.

Contribution

It provides a detailed calculation of spin-drag relaxation rates in various dimensions and explores their behavior near ferromagnetic phase transitions in ultracold Fermi mixtures.

Findings

In 1D, the relaxation rate vanishes linearly with temperature.

In 3D, the relaxation rate vanishes quadratically with temperature for weak interactions.

Spin fluctuations enhance the relaxation rate near the ferromagnetic transition.

Abstract

We calculate the spin-drag relaxation rate for a two-component ultracold atomic Fermi gas with positive scattering length between the two spin components. In one dimension we find that it vanishes linearly with temperature. In three dimensions the spin-drag relaxation rate vanishes quadratically with temperature for sufficiently weak interactions. This quadratic temperature dependence is present, up to logarithmic corrections, in the two-dimensional case as well. For stronger interaction the system exhibits a Stoner ferromagnetic phase transition in two and three dimensions. We show that the spin-drag relaxation rate is enhanced by spin fluctuations as the temperature approaches the critical temperature of this transition from above.