Microscopic theory of spin-orbit and spin-tranfer torques in Rashba ferromagnets and beyond

Abstract: Spin-orbit and spin-transfer torques are competing forces that drive magnetic domains in the heavy-metal/ferromagnet bi-layers in the presence of electric current. In this talk I present a microscopic theory of both effects that is obtained from generalised Kubo formalism for a disordered electron system and completely avoids the notion of spin currents and spin Hall effect. I also treat the Gilbert damping on the same footing. In this formalism the torques are naturally related to susceptibility tensors that can be evaluated microscopically for a given model. In this talk I mainly focus on the torques arising in a heavy-metal/ferromagnet bilayers and demonstrate that spin-orbit interactions are generally responsible for a giant enhancement of spin transfer toques. I show that as the result of spin-orbit coupling the so-called beta torque is naturally decoupled to the in-plane and out-of plane components that may be different by several orders of magnitude. The same behaviour is characteristic for the Gilbert damping. If time allows I also discuss various applications of the theory to the spin torques arising in antiferromagnets and heterostructures involving Weyl semimetals and topological insulators.