Oscillatory Dyakonov-Perel spin dynamics in two-dimensional electron gases

Optical pump-probe measurements of spin dynamics at temperatures down to 1.50.3em0exK are described for a series of (001)-oriented GaAs∕AlGaAs quantum well samples containing high mobility two-dimensional electron gases (2DEGs). For well widths ranging from 50.3em0exto0.3em0ex200.3em0exnm and 2DEG sheet densities from $1.75×{}{10}¹¹{{0.3em}{0ex}}to{{0.3em}{0ex}}3.5×{}{10}¹¹{{0.3em}{0ex}}{cm}^{{-}2}$, the evolution of a small injected spin population is found to be a damped oscillation rather than an exponential relaxation, consistent with the quasi-collision-free regime of the Dyakonov-Perel spin dynamics. A Monte Carlo simulation method is used to extract the spin-orbit-induced electron spin precession frequency Ω(kF) and electron momentum scattering time τₚ* at the Fermi wave vector. The spin decay time passes through a minimum at a temperature corresponding to the transition from collision-free to collision-dominated regimes and τₚ* is found to be close to the ensemble momentum scattering time τₚ obtained from Hall measurements of electron mobility. The values of Ω(kF) give the Dresselhaus or bulk inversion asymmetry (BIA) coefficient of spin-orbit interaction as a function of electron confinement energy in the quantum wells and show, qualitatively, the behavior expected from $k∙p$ theory.