Spin–orbit torques due to topological insulator surface states: an in-plane magnetization as a probe of extrinsic spin–orbit scattering

Abstract

Abstract Topological insulator (TI) surface states exert strong spin–orbit torques. When the magnetization is in the plane its interaction with the TI conduction electrons is non-trivial, and is influenced by extrinsic spin–orbit scattering. This is expected to be strong in TIs but is difficult to calculate and to measure unambiguously. Here we show that extrinsic spin–orbit scattering sizably renormalizes the surface state spin–orbit torque resulting in a strong density dependence. The magnitude of the renormalization of the spin torque and the effect of spin–orbit scattering on the relative sizes of the in-plane and out-of-plane field-like torques have strong implications for experiment: We propose two separate experimental signatures for the measurement of its presence.