Exciton spin dynamics in diluted magnetic semiconductor quantum wells

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In this project we aim to develop a microscopic, quantum-kinetic theory for the spin dynamics in diluted magnetic semiconductor nanostructures accounting for both, correlations due to the exchange coupling with magnetic dopants as well as the Coulomb interaction, which in particular gives rise to excitonic correlations. The considered technologically important systems are especially promising in terms of innovative applications based on the active use of correlations and quantum coherent dynamical phenomena. This applies in particular to applications in information technology that require a coherent spin control. The basis for future progress in this direction is a deepened understanding of spin dynamics which requires a theory beyond the current state-of-the-art. As a first application of our new theory we shall try to identify quantum kinetic signatures in the spin dynamics of excitonic excitations in quantum wells. These studies will advance the understanding of spin relaxation and should provide insight concerning the role of quantum coherences for spin relaxation. In particular, we shall explore in how far the spin relaxation deviates from an incoherent process that can be modelled by rate equations. In this context we shall also analyze the impact of energetic redistributions between different excitonic states on the spin dynamics.A further focus of the research within this project is the analysis of the interplay between influences of the exchange interaction with magnetic dopants and the spin-orbit coupling of optically excited carriers on the spin dynamics. In diluted magnetic semiconductors usually the exchange interaction dominates. However, varying suitable material parameters in particular in multi-component composite semiconductors allows for tailoring the relative strengths of these interactions in a wide range. Even situations where both couplings are of comparable strength can be realized. Studies of excitations of free carriers in the latter regime give rise to the expectation that also in the case of excitonic excitations a qualitatively new dynamical behavior of the spin system should arise when both couplings are comparable. This could pave the way towards new approaches of spin control.Another target is to explore the possibilities to control the spin dynamics by exciting excitonic states using light with well-defined orbital angular momentum ('twisted light'). This part of the project shall shed light on the question whether the use of novel types of light sources, such as twisted light, that are a focus of topical research opens new ways for the external manipulation of spins that differ from traditional methods as, e. g., the spin orientation via circularly polarized conventional laser light.