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

TL;DR

This paper investigates how extrinsic spin-orbit scattering influences the spin-orbit torques on topological insulator surface states with in-plane magnetization, revealing significant density-dependent effects and proposing experimental detection methods.

Contribution

It demonstrates that extrinsic spin-orbit scattering significantly renormalizes surface state spin-orbit torques and suggests experimental signatures for detection.

Findings

Spin-orbit scattering causes strong density-dependent renormalization of spin torque.

The relative sizes of in-plane and out-of-plane torques are affected by spin-orbit scattering.

Two experimental signatures are proposed to measure the effects of extrinsic spin-orbit scattering.

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.