Spin Drag and Spin-Charge Separation in Cold Fermi Gases

TL;DR

This paper explores how spin and charge excitations in one-dimensional cold Fermi gases not only propagate at different velocities but also experience different damping, with spin excitations being intrinsically damped and diffusive, unlike charge excitations.

Contribution

It reveals that spin and charge modes have distinct damping rates, adding a new dimension to the understanding of spin-charge separation in cold Fermi gases.

Findings

Charge excitations are ballistic with minimal damping.

Spin excitations are intrinsically damped and diffusive.

Cold Fermi gases can be used to measure spin-drag relaxation rates.

Abstract

Low-energy spin and charge excitations of one-dimensional interacting fermions are completely decoupled and propagate with different velocities. These modes however can decay due to several possible mechanisms. In this paper we expose a new facet of spin-charge separation: not only the speeds but also the damping rates of spin and charge excitations are different. While the propagation of long-wavelength charge excitations is essentially ballistic, spin propagation is intrinsically damped and diffusive. We suggest that cold Fermi gases trapped inside a tight atomic waveguide offer the opportunity to measure the spin-drag relaxation rate that controls the broadening of a spin packet.