Quantum kinetic description of spin transfer in diluted magnetic semiconductors

Abstract

We derive quantum kinetic equations of motion that describe laser-driven Mn-doped diluted semiconductors and account for the carrier Mn exchange interaction beyond the mean-field theory. We treat a spatially inhomogeneous system with arbitrary given positions of Mn dopants as well as an ensemble of randomly distributed Mn atoms in an infinite crystal, which represents an on average spatially homogeneous system. In the latter case, special care is taken of the interplay between higher-order correlations and the random positioning of Mn atoms. For the ensemble-averaged system, we explicitly identify the terms responsible for a spin transfer between spin-polarized carriers and Mn atoms in the special case valid, e.g., for paramagnetic samples without external magnetic field, where initially the total Mn magnetization vanishes. It turns out that here the mean-field approach as well as the virtual crystal approximation predict a vanishing spin transfer, in contrast to our quantum kinetic equations. Moreover, in our approach, the exchange interaction with the localized Mn atoms leads to a significant redistribution of the carrier momenta even in an on average spatially homogeneous system. The latter feature can not be described in the virtual crystal approximation.