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

Abstract

AbstractWe show a systematic study on cooling and spin‐relaxation dynamics of spin‐polarized excitons in a diluted magnetic semiconductor quantum well of Cd0.95Mn0.05Te, 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 sublevels 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 phonon scattering and emission in the electron‐spin relaxation are pointed out, in addition to a spin‐flip process induced by local Mn spins via s‐d exchange interaction. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)