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

Abstract

We have studied the spin dynamics of a high-mobility two-dimensional electron system in a GaAs/Al0.3Ga0.7As 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, T2 *, increases from about 20 to 200 ps. Moreover, T2 * 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 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 Dyakonov- Perel and the Bir-Aronov-Pikus mechanisms, with 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.