Theory of excitation and relaxation of magnetic systems in the femto-second range

寻找和理解固态系统中磁化逆转的基本时间限制是目前磁学中最具启发性的问题之一。理论物理学目前还没有明确的程序或概念来回答这个问题。相反，概念必须发展。我们将讨论飞秒激光脉冲局部激发磁系统后磁化强度变化的物理根源。由于激光场和内部库仑相互作用都不能改变磁化，显然需要一种打破自旋守恒的机制。讨论集中在两个最明显的候选：自旋-轨道相互作用和自旋-晶格弛豫。我们想通过一个时间相关的Schrödinger方程来研究它们在激发期间对磁化的影响，并通过两个自旋通道的玻尔兹曼方程来研究它们在弛豫期间对磁化的影响。

Finding and understanding the fundamental time limits for the magnetization reversal in a solid state system is currently one of the most inspiring questions in magnetism. Theoretical physics has currently no clear cut procedure or concept at hand to answer this question. Instead concepts have to be developed. We will address the physical origin of the change of the magnetization after a local excitation of a magnetic system by femto-second laser pulse. As neither the laser field nor internal Coulomb interactions are able to alter the magnetization, apparently a mechanism breaking the spin conservation is necessary. The discussion concentrates on the two most obvious candidates: the spin-orbit interaction and the spin-lattice relaxation. We want to study their influence on the magnetisation during the excitation via a time-dependent Schrödinger equation and in the period of relaxation afterwards via a Boltzmann equation for the two spin channels.