Cooling and spin-relaxation dynamics of spin-polarized excitons in a diluted magnetic semiconductor quantum well

摘要

We show a systematic study on cooling and spin-relaxation dynamics of spin-polarized excitons in a diluted magnetic semiconductor quantum well of Cd_(0.95)Mn_(0.05)Te, by means of pump-probe absorption spectroscopy under magnetic fields. Time dependences of circularly polarized saturation absorption intensities after optical pumping showed the dynamics of carrier cooling and spin relaxation at spin-split exciton sub-rnlevels at various magnetic fields. Spin-polarized electrons at a higher-energy up-spin state relax to a lower-energy down-spin one with time constants ranging from 6 to 20 ps, depending on the magnetic field. Roles of phoaon scattering and emission in the electron-spin relaxation are pointed out, in addition to a spin-flip process induced 6y local Mn spins via s-d exchange interaction.