Stable spin domains in a non-degenerate ultra-cold gas

TL;DR

This paper investigates the stability of spin domains in a non-degenerate ultra-cold gas of rubidium atoms, revealing how magnetic field gradients and spin wave dynamics contribute to domain stabilization.

Contribution

It introduces a mechanism for stabilizing spin domains using magnetic field gradients and analyzes the decoupling of magnetization dynamics in a non-degenerate ultra-cold gas.

Findings

Magnetic field gradients stabilize spin domains via collective spin rotation.

Longitudinal magnetization remains static within domains.

Transverse spin waves are confined within domain walls.

Abstract

We study the stability of two-domain spin structures in an ultra-cold gas of magnetically trapped $^{87}$Rb atoms above quantum degeneracy. Adding a small effective magnetic field gradient stabilizes the domains via coherent collective spin rotation effects, despite negligibly perturbing the potential energy relative to the thermal energy. We demonstrate that domain stabilization is accomplished through decoupling the dynamics of longitudinal magnetization, which remains in time-independent domains, from transverse magnetization, which undergoes a purely transverse spin wave trapped within the domain wall. We explore the effect of temperature and density on the steady-state domains, and compare our results to a hydrodynamic solution to a quantum Boltzmann equation.