Effect of initial spin polarization on spin dephasing and electron g factor in a high-mobility two-dimensional electron system

TL;DR

This study explores how initial spin polarization affects spin dephasing and electron g factor in a high-mobility 2D electron system, revealing significant increases in spin lifetime and decreases in g factor with higher polarization, explained by Coulomb interactions.

Contribution

It provides the first detailed experimental and theoretical analysis of the dependence of spin dephasing and g factor on initial spin polarization in a 2DES.

Findings

Spin dephasing time increases from 20 ps to 200 ps with polarization.

Electron g factor decreases as polarization increases.

Coulomb interactions via Hartree-Fock dominate the observed effects.

Abstract

We have investigated the spin dynamics of a high-mobility two-dimensional electron system (2DES) in a GaAs--Al$_{0.3}$Ga$_{0.7}$As single quantum well by time-resolved Faraday rotation (TRFR) in dependence on the initial degree of spin polarization, $P$, of the 2DES. From $P\sim 0$ to $P\sim 30$ %, we observe an increase of the spin dephasing time, $T_2^\ast$, by an order of magnitude, from about 20 ps to 200 ps, in good agreement with theoretical predictions by Weng and Wu [Phys. Rev. B {\bf 68}, 075312 (2003)]. Furthermore, by applying an external magnetic field in the Voigt configuration, also the electron $g$ factor is found to decrease for increasing $P$. Fully microscopic calculations, by numerically solving the kinetic spin Bloch equations considering the D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms, reproduce the most salient features of the experiments, {\em i.e}., a dramatic decrease of spin dephasing and a moderate decrease of the electron $g$ factor with increasing $P$. We show that both results are determined dominantly by the Hartree-Fock contribution of the Coulomb interaction.