Nonequilibrium quantum dynamics of current-driven magnetic skyrmions

点击翻译按钮获取中文摘要

The topological protection of magnetic Skyrmions renders them interesting candidates for the reliable processing of information in technological racetrack devices. Skyrmions are vortex-like spin textures with non-collinear magnetization that can be formed in non-centrosymmetric magnetic compounds. They are viewed as quasiparticles that are rather stable, can be small in size down to the atomic scale and can be moved by low densities of spin-polarized electronic currents. Their formation and their control are nontrivial dynamical processes (due to topological protection) and require nonequilibrium processes involving dissipation, as we have described in the previous funding period. Moreover, their dynamics in the presence of impurity clusters shows a variety of phenomena described in the report. While well advanced dynamical simulations have been carried out in the past, we intend in the coming funding period to address the question of the dynamical stability of Skyrmions and Antiskyrmions in terms of a potential energy landscape in the presence of an external current as a function of suitable deformation parameters. We aim to obtain a Kramers rate theory for the stability of the Skyrmions. Furthermore, we will turn our focus to antiferromagnetic Skyrmions which are interesting because in addition to the mentioned features of Skyrmions, an antiferromagnetic host with zero total magnetization is magnetically rather inert, yet on the cost that an external manipulation by a current is non-trivial. Especially the presence of a current which drives the system away from its groundstate motivates a theoretical description of the antiferromagnet beyond mean-field theory for two coupled ferromagnetic sublattices. We plan to develop such a theory of current-driven antiferromagnetic Skyrmions beyond mean-field theory by extending the latter by spin-wave fluctuations. We foresee novel contributions to the spin transfer torque. Moreover, we shall study real quantum Skyrmions formed by quantum spins residing at the lattice sites. We intend to extend our preliminary quantum simulations, addressing the questions of stability and the interplay of quantum mechanics with the classical concept of topology. Finally, we plan to investigate the dynamics of magnetic Skyrmions driven by circular spin waves from point-like emitters. This concept is technologically relevant for potential devices and is also studied experimentally in the project of Dr. Stefan Krause (Universität Hamburg) with whom we plan to collaborate in the present Priority Programme.