Nonlocal Spin Dynamics Arising From Induced Interactions at the Interface of a Topological Insulator and a Ferromagnet

In recent years, topologically stable magnetic textures called skyrmions have received much attention for their potential uses in information technology. One such use is making skyrmions the information carriers in low-dissipation information storage devices because skyrmions can be moved using exceedingly small currents. One proposed setup is to move them using a low-dissipation current on the surface of a topological insulator. In this work, an effective field theory for the spins in such a heterostructure is derived. The theory shows time-dependent induced spin-spin interactions such as DMI and the presence of nonnegligible retardation effects which alter the system's spin dynamics. In particular, we derive an inertial term and various dissipative terms in the Landau-Lifshitz-Gilbert equation. This work was funded by the Research Council of Norway (RCN) through its Centres of Excellence funding scheme Project No. 262633, ``QuSpin,'' and RCN Project No. 323766, ``Equilibrium and out-of-equilibrium quantum phenomena in superconducting hybrids with antiferromagnets and topological insulators.''