The ever-increasing demand for data and computing power ignited by datadriven technology raises the desire for a new generation of faster and more efficient computing devices. Furthermore, the sheer amount of data generated requires storage devices to pack information as dense as possible. Emerging data processing techniques, such as machine learning, call for a new generation of computing devices. The field of ultrafast spintronics has emerged as aviable candidate to address these challenges. Within spintronics the electric charge is superseded by the electrons spin degree of freedom as information carrier. Antiferromagnetic materials are of special interest in this context, due to their fast internal dynamics in the THz regime and their robustness with respect to stray fields, which allows for dense packaging of individual memory domains. To overcome conventional electronics and leverage the potential THz speeds of antiferromagnetic spintronic devices an all optical control of these devices is paramount. One key challenge is to identify viable material candidates and this thesis aims to support this task by providing the computational tools to calculate second order responses to femtosecond laser pulses. In this thesis a highly parallelized Wannier interpolation code was developed capable of calculating second order response tensors by means of the Keldysh non-equilibrium formalism. With the developed method second order effects such as photocurrents of charge and spin as well as the inverse Faraday effect can be calculated. Furthermore, the orbital equivalents of the aforementioned spin effects can be calculated. The developed methods were applied to study second order laser responses in various magnetic materials and the analysis demonstrated that charge photocurrents act as a good proxy to measure the orientation of the magnetic moments. The emergence of chiral photocurrents in canted antiferromagnets suggests that photocurrent scan also be used to track the switching process of the Néel vector. A largest aggered inverse Faraday effect was found on the Mn sublattices of Mn2Ausuggesting that efficient direct switching of the order parameter is possible in this material. Further, a non-linear optical equivalent to the spin Hall effect, dubbed the photospin Hall effect, was discovered in collinear antiferromagnetMn2Au. Finally, canted Mn2Au was found to host gigantic spin photocurrents, making the material a good candidate for practical spintronic device applications.
Maximilian Daniel Merte (Wed,) studied this question.