Dependence of spin dephasing on initial spin polarization in a high-mobility two-dimensional electron system

TL;DR

This study investigates how initial spin polarization affects spin dephasing times in high-mobility 2D electron systems, combining experimental measurements with microscopic theoretical calculations to reveal polarization-dependent spin dynamics.

Contribution

It provides the first comprehensive experimental and theoretical analysis of the dependence of spin dephasing on initial spin polarization in high-mobility 2D electron systems.

Findings

Spin dephasing time increases with initial spin polarization.

Temperature dependence of spin dephasing varies with polarization.

Theoretical calculations agree with experimental results.

Abstract

We have studied the spin dynamics of a high-mobility two-dimensional electron system in a GaAs/Al_{0.3}Ga_{0.7}As single quantum well by time-resolved Faraday rotation and time-resolved Kerr rotation in dependence on the initial degree of spin polarization, P, of the electrons. By increasing the initial spin polarization from the low-P regime to a significant P of several percent, we find that the spin dephasing time, $T_2^\ast$, increases from about 20 ps to 200 ps; Moreover, $T_2^\ast$ increases with temperature at small spin polarization but decreases with temperature at large spin polarization. All these features are in good agreement with theoretical predictions by Weng and Wu [Phys. Rev. B {\bf 68}, 075312 (2003)]. Measurements as a function of spin polarization at fixed electron density are performed to further confirm the theory. A fully microscopic calculation is performed by setting up and numerically solving the kinetic spin Bloch equations, including the D'yakonov-Perel' and the Bir-Aronov-Pikus mechanisms, with {\em all} the scattering explicitly included. We reproduce all principal features of the experiments, i.e., a dramatic decrease of spin dephasing with increasing $P$ and the temperature dependences at different spin polarizations.