Non-linear antidamping spin-orbit torque originating from intra-band transport on the warped surface of a topological insulator

TL;DR

This paper reveals that a strong, non-linear antidamping spin-orbit torque on topological insulator surfaces arises from intraband transitions, significantly exceeding linear response predictions and explaining recent experimental observations.

Contribution

It demonstrates that non-linear intra-band transport, influenced by warping and magnetization, can produce large antidamping SOT without interband transitions, advancing understanding of spin-orbit effects.

Findings

Non-linear intra-band transitions generate strong antidamping SOT.

Warping and in-plane magnetization enhance the SOT magnitude.

Nonlinear SOT can surpass linear response predictions by orders of magnitude.

Abstract

Motivated by recent experiments observing a large antidamping spin-orbit torque (SOT) on the surface of a three-dimensional topological insulator, we investigate the origin of the current-induced SOT beyond linear-response theory. We find that a strong antidamping SOT arises from intraband transitions in non-linear response, and does not require interband transitions as is the case in linear transport mechanisms. The joint effect of warping and an in-plane magnetization generates a non-linear antidamping SOT which can exceed the intrinsic one by several orders of magnitude, depending on warping parameter and the position of Fermi energy, and exhibits a complex dependence on the azimuthal angle of the magnetization. This nonlinear SOT provides an alternative explanation of the observed giant SOT in recent experiments.