Spin-rotation mode in a quantum Hall ferromagnet

TL;DR

This paper investigates a spin-rotation mode in a quantum Hall ferromagnet, analyzing its microscopic dynamics, damping mechanisms, and the role of spin excitons, revealing a distinct relaxation process involving Goldstone and spin-wave excitons.

Contribution

It introduces a microscopic description of the spin-rotation mode and identifies a novel damping mechanism linked to spatial fluctuations of the Landé g-factor.

Findings

The spin-rotation mode is a superposition of eigenstates with different S_z values.

Damping is caused by spin stochastization due to g-factor fluctuations.

Transverse spin relaxation occurs without affecting the S_z number.

Abstract

A spin-rotation mode emerging in a quantum Hall ferromagnet due to laser pulse excitation is studied. This state, macroscopically representing a rotation of the entire electron spin-system to a certain angle, is not microscopically equivalent to a coherent turn of all spins as a single-whole and is presented in the form of a combination of eigen quantum states corresponding to all possible S_z spin numbers. The motion of the macroscopic quantum state is studied microscopically by solving a non-stationary Schroedinger equation and by means of a kinetic approach where damping of the spin-rotation mode is related to an elementary process, namely, transformation of a `Goldstone spin exciton' to a `spin-wave exciton'. The system exhibits a spin stochastizationa mechanism (determined by spatial fluctuations of the Land'e g-factor) ensuring damping, transverse spin relaxation, but irrelevant to decay of spin-wave excitons and thus not involving longitudinal relaxation, i.e., recovery of the S_z number to its equilibrium value.