Electrically-induced spin torques due to the bulk states of topological insulators

James H. Cullen, Rhonald Burgos Atencia, Dimitrie Culcer

Published 2022-06-20Version 1

The relative contributions of bulk and surface states to the spin torque at topological insulator (TI)/ferromagnet interfaces are poorly understood. Here we study spin torques due to TI bulk states and show that: (i) There is no spin torque on a homogeneous magnetization; (ii) There is a spin transfer torque on an inhomogeneous magnetization, which is small in our idealized model but may be sizable in real samples; (iii) There is no bulk spin-Hall effect. A smoking gun for experiment is the comparable size of the spin transfer torque for in-plane and out-of-plane magnetizations.