Identification and control of ultrafast spin dynamics in ferromagnetic solids by tailored fields

我们分析了自旋动力学在外延过渡金属铁磁薄膜和界面驱动强电磁场，并旨在通过优化和定制的驱动强场在可见光和红外光谱区控制的动态。在我们合作的理论和实验项目的框架内，我们进行了一个完全从头算的含时密度泛函理论研究飞秒（fs）激光诱导的退磁，我们利用这种现象，以调查电子电荷和自旋动力学，特别强调自旋相关的电荷转移，自旋轨道相互作用和耦合到核运动。同时，我们进行了实验研究，采用飞秒时间分辨的线性和非线性磁光。这使我们能够分析动态自旋相关的影响，由于自旋-轨道耦合，电子散射与声子和磁激发，和自旋转移和运输的影响所引起的外部施加的电磁场，驱动铁磁体远离平衡。在第一个资助期内，我们已经确定了自旋相关的电荷转移和自旋轨道耦合介导的自旋翻转的超快退磁的Co/Cu（001）由于我们协调的实验和理论的努力。在此基础上，我们将设计激光脉冲来优化控制自旋动力学。然后，这些最佳脉冲将用于我们的实验工作，以进一步验证和开发。基于我们新开发的长程物理模型，我们将开发一个核动力学代码，它完全耦合到现有的自旋-电荷-动力学代码（http：elk.sourceforge.net）。在第一个资助期内，我们已经证明量子最优控制可以与后一个代码连接，从而可以定制激光脉冲。进一步的剪裁将通过对目标泛函采用实验约束来完成。在实验部分，我们将进一步提高时间分辨率，使用非共线光参量放大产生的亚15 fs脉冲，并使用光参量啁啾脉冲放大将驱动激光场的强度提高到10^15 W/cm ^2。识别实验观察到的签名与微观过程和理论上的最佳脉冲设计，从而使脉冲整形操纵和控制自旋动力学向所需的响应驱动定制的强电磁场。

We analyze spin dynamics in epitaxial transition metal ferromagnetic films and at interfaces driven by intense electromagnetic fields and aim at controlling the dynamics by optimizing and tailoring the driving intense fields in the visible and infrared spectral region. In the framework of our collaborative theoretical and experimental project we perform a fully ab-initio time-dependent density functional theory investigation of femtosecond (fs) laser induced demagnetization, a phenomenon which we exploit in order to investigate the electronic charge and spin dynamics with particular emphasis on spin-dependent charge transfer, spin-orbit interaction and coupling to nuclear motion. Simultaneously, we carry out an experimental investigation employing fs time-resolved linear and non-linear magneto-optics. This allows us to analyze dynamic spin-dependent effects due to spin-orbit coupling, electronic scattering with phononic and magnetic excitations, and spin transfer and transport effects induced by the externally applied electromagnetic fields, which drive the ferromagnet far out of equilibrium. In the first funding period, we have identified spin-dependent charge transfer and spin-orbit coupling mediated spin flips in the ultrafast demagnetization of Co/Cu(001) due to our coordinated experimental-theoretical effort. On this basis, we will design laser pulses to optimally control the spin-dynamics. These optimal pulses will then be used in our experimental effort for further validation and development. Based on our newly developed ansatz for long-range physics, we will develop a nuclear dynamics code, which is fully coupled to the already existing spin-charge-dynamics code (http://elk.sourceforge.net). In the first funding period, we have demonstrated that quantum optimal control can be interfaced to the latter code such that laser pulses can be tailored. Further tailoring will be done by employing experimental constraints on the target functionals. Within the experimental part we will further improve the time resolution using sub 15 fs pulses generated by non-collinear optical parametric amplification and increase the intensity of driving laser fields up to 10^15 W/cm^2 employing optical parametric chirped pulse amplification. Identification of experimentally observed signatures with microscopic processes and the theoretical optimal pulse design will thus enable pulse shaping to manipulate and control the spin dynamics towards a desired response driven by tailored intense electromagnetic fields.