Electron charge and spin delocalization revealed in the optically probed longitudinal and transverse spin dynamics in n-GaAs

摘要

The evolution of the electron spin dynamics as consequence of carrier delocalization in n-type GaAs is investigated by the recently developed extended pump-probe Kert/Faraday rotation spectroscopy. We find that isolated electrons localized on donors demonstrate a prominent difference between the longitudinal and transverse spin relaxation rates in a magnetic field, which is almost absent in' the metallic phase. The inhomogeneous transverse dephasing time T_2~* of the spin ensemble strongly increases upon electron delocalization as a result of motional narrowing that can be induced by increasing either the donor concentration or the temperature. An unexpected relation between T_2 and the longitudinal spin relaxation time T_1 is found, namely, that their product is about constant, as explained by the magnetic field effect on the spin diffusion. We observe a two-stage longitudinal spin relaxation, which suggests the establishment of spin temperature in the system of exchange-coupled donor-bound electrons.