Giant orbital Hall effect due to the bulk states of 3D topological insulators

TL;DR

This paper demonstrates that bulk states in 3D topological insulators produce a giant orbital Hall effect, significantly larger than the spin Hall effect, which can enhance magnetic torque efficiency in spintronic devices.

Contribution

It reveals that bulk states in topological insulators generate a large orbital Hall effect, surpassing the spin Hall effect, and suggests engineering heterostructures to optimize orbital-to-spin conversion.

Findings

Orbital Hall effect in topological insulators is up to 1000 times larger than the spin Hall effect.

Bulk states carry orbital angular momentum much greater than the electron spin.

Enhanced orbital effects can improve torque efficiency in magnetic devices.

Abstract

The highly efficient torques generated by 3D topological insulators make them a favourable platform for faster and more efficient magnetic memory devices. Recently, research into harnessing orbital angular momentum in orbital torques has received significant attention. Here we study the orbital Hall effect in topological insulators. We find that the bulk states give rise to a sizeable orbital Hall effect that is up to 3 orders of magnitude larger than the spin Hall effect in topological insulators. This is partially because the orbital angular momentum that each conduction electron carries is up to an order of magnitude larger than the $\hbar/2$ carried by its spin. Our results imply that the large torques measured in topological insulator/ferromagnet devices can be further enhanced through careful engineering of the heterostructure to optimise orbital-to-spin conversion.