Spin evolution in a two-dimensional electron gas after laser excitation

The femtosecond laser excitation of the spin configuration in a low-dimensional magnetic semiconductor is investigated. An atomistic Schrodinger model is developed in which trapped electrons and ionic impurities are coupled via exchange interactions. By defining a suitable set of non-Hermitian operators, the microscopic Schrodinger description of the particles is combined with the more phenomenological Landau-Bloch relaxation mechanism. Differing from the standard approaches, in this model the statistical widths of the wave functions become time-dependent. This enables the study of decoherence effects where the evolution of the system, from an initial pure state to a final mixed state, is induced by the spin interaction. Simulations reproduce the out-of-equilibrium spin evolution observed in ZnCdSe devices. The effects of quantum confinement and multimode excitation are discussed.