Ultrafast spin dynamics in II-VI diluted magnetic semiconductors with spin-orbit interaction

摘要

We study theoretically the ultrafast spin dynamics of II-VI diluted magneticsemiconductors in the presence of spin-orbit interaction. Our goal is toexplore the interplay or competition between the exchange $sd$-coupling and thespin-orbit interaction in both bulk and quantum well systems. For bulkmaterials we concentrate on Zn$_{1-x}$Mn$_x$Se and take into account theDresselhaus interaction, while for quantum wells we examineHg$_{1-x-y}$Mn$_x$Cd$_y$Te systems with a strong Rashba coupling. Ourcalculations were performed with a recently developed formalism whichincorporates electronic correlations beyond mean-field theory originated fromthe exchange $sd$-coupling. For both bulk and quasi-two-dimensional systems wefind that, by varying the system parameters within realistic ranges, bothinteractions can be chosen to play a dominant role or to compete on an equalfooting with each other. The most notable effect of the spin-orbit interactionin both types of systems is the appearance of strong oscillations where theexchange $sd$-coupling by itself only causes an exponential decay of the meanelectronic spin components. The mean-field approximation is also studied and itis interpreted analytically why it shows a strong suppression of thespin-orbit-induced dephasing of the spin component parallel to the Mn magneticfield.