Spin precession and spin waves in a chiral electron gas: beyond Larmor's theorem

TL;DR

This paper investigates how spin-orbit coupling affects spin precession and spin waves in a quasi-two-dimensional electron gas, revealing deviations from traditional Larmor's theorem and providing precise experimental parameter extraction.

Contribution

It introduces a linear-response density-functional theory approach to analyze spin-wave dispersions beyond Larmor's theorem, including analytic results and experimental parameter extraction.

Findings

Analytic spin-wave dispersion relations for small wave vectors

Accurate extraction of Rashba and Dresselhaus coupling strengths from experiments

Significant deviations from local density approximation in spin-dependent systems

Abstract

Larmor's theorem holds for magnetic systems that are invariant under spin rotation. In the presence of spin-orbit coupling this invariance is lost and Larmor's theorem is broken: for systems of interacting electrons, this gives rise to a subtle interplay between the spin-orbit coupling acting on individual single-particle states and Coulomb many-body effects. We consider a quasi-two-dimensional, partially spin-polarized electron gas in a semiconductor quantum well in the presence of Rashba and Dresselhaus spin-orbit coupling. Using a linear-response approach based on time-dependent density-functional theory, we calculate the dispersions of spin-flip waves. We obtain analytic results for small wave vectors and up to second order in the Rashba and Dresselhaus coupling strengths $\alpha$ and $\beta$. Comparison with experimental data from inelastic light scattering allows us to extract $\alpha$ and $\beta$ as well as the spin-wave stiffness very accurately. We find significant deviations from the local density approximation for spin-dependent electron systems.