Carrier-impurity spin transfer dynamics in paramagnetic Ⅱ-Ⅵ diluted magnetic semiconductors in the presence of a wave-vector-dependent magnetic field

摘要

Quantum kinetic equations of motion for carrier and impurity spins in paramagnetic Ⅱ-Ⅵ diluted magnetic semiconductors in a k-dependent effective magnetic field are derived, where the carrier-impurity correlations are taken into account. In the Markov limit, rates for the electron-impurity spin transfer can be derived for electron spins parallel and perpendicular to the impurity spins corresponding to measurable decay rates in Kerr experiments in Faraday and Voigt geometry. Our rigorous microscopic quantum kinetic treatment automatically accounts for the fact that, in an individual spin flip-flop scattering process, a spin flip of an electron is necessarily accompanied by a flop of an impurity spin in the opposite direction and the corresponding change of the impurity Zeeman energy influences the final energy of the electron after the scattering event. This shift in the electron energies after a spin flip-flop scattering process, which usually has been overlooked in the literature, turns out to be especially important in the case of extremely diluted magnetic semiconductors in an external magnetic field. As a specific example for a k-dependent effective magnetic field the effects of a Rashba field on the dynamics of the carrier-impurity correlations in a Hg_(1-x-y)Cd_yMn_xTe quantum well are described. It is found that, although accounting for the Rashba interaction in the dynamics of the correlations leads to a modified k-space dynamics, the time evolution of the total carrier spin is not significantly influenced. Furthermore, a connection between the present theory and the description of collective carrier-impurity precession modes is presented.