Quantum kinetic theory of ultrafast phenomena in diluted magnetic semiconductors

该项目致力于稀磁半导体（DMS）中超快现象的理论研究，旨在促进对DMS中基本物理过程的理解，如超快时间尺度上的自旋和轨道角动量转移。我们的目标是确定对先进技术应用感兴趣的量子动力学机制，例如，短时间内磁性能的相干控制。该项目的具体目标有三个方面。首先，阐明了自旋轨道相互作用与RKKY型交换相互作用在自由载流子与磁性杂质之间的自旋转移中的竞争。第二，探索由具有轨道角动量的光（扭曲光）和强单周期太赫兹脉冲激发所带来的相干量子控制的可能性。最后，研究了电子-电子相互作用在限制DMS角动量转移相干操作的退相干过程中的作用。方法的出发点是最近发展的量子动力学密度矩阵描述的交换诱导的DMS中的自旋转移。这一理论应加以扩展，以包括额外的自旋-轨道和电子-电子相互作用，以及耦合到扭曲的光。如果在项目的过程中，它被证明是必要的，也可以使用非平衡绿色函数技术。新开发的扩展方程的适用性应通过数值研究来证明，这些研究揭示了物理含义，并允许将预测与现实（现有或拟议）实验情况进行比较。

This project is devoted to theoretical studies of ultrafast phenomena in diluted magnetic semiconductor (DMS) which are targeted at advancing the understanding of basic physical processes in DMS such as spin and orbital-angular-momentum transfer on ultrafast time scales. We aim to identify quantum-kinetic mechanisms that are of interest for advanced technological applications, e.g., the coherent control of magnetic properties on short times. The specific objectives of the project are three-fold. First, to elucidate the competition of the spin-orbit interaction with RKKY-type exchange interactions in the spin transfer between free carriers and magnetic impurities. Second, to explore the coherent quantum control possibilities brought about by excitation with light with orbital angular momentum (twisted light) and intense single-cycle terahertz pulses. And finally, to investigate the role of the electron-electron interaction in the decoherence processes that limit the coherent manipulation of angular-momentum transfer in DMS. The methodic starting point is a recently developed quantum kinetic density matrix description of the exchange induced spin-transfer in DMS. This theory shall be extended to include additionally the spin-orbit and electron-electron interaction as well as the coupling to twisted light. If in the course of the project it turns out to be necessary, also non-equilibrium Green's function techniques may be used. The applicability of the newly developed extended equations shall be demonstrated by numerical studies that reveal the physical implications and allow for a comparison of the predictions with realistic (existing or proposed) experimental situations.