EXCITON SPIN DYNAMICS IN GAAS QUANTUM-WELLS

We have investigated the temperature dependence of the exciton spin re laxation between 10 and 300 K in undoped GaAs quantum wells by using t he nonlinear transmission pump-probe and the four-wave-mixing techniqu es. The electron spin relaxation rate above 40 K is found to be propor tional to the product of the temperature and the momentum relaxation t ime, which indicates that the D'yakonov-Perel' interaction governs the spin-flip dynamics. The temperature independence below 30 K is consid ered to be due to the band-mixing effect that determines the hole spin relaxation, and the spin exchange is effective to the exciton spin re laxation in these temperatures.