Spin and Charge Transport on the Surface of a Topological Insulator

TL;DR

This paper derives diffusion equations for spin-charge transport on topological insulator surfaces, predicts a novel magnetoresistance effect influenced by spin polarization and gate voltage, and suggests potential transistor applications.

Contribution

It introduces a new set of diffusion equations capturing strong spin-charge coupling on topological insulator surfaces and predicts a novel, tunable magnetoresistance effect.

Findings

Prediction of a nonohmic voltage correction proportional to spin polarization and current.

Demonstration of gate voltage tunability of the magnetoresistance effect.

Proposal of a device operation as a transistor based on the effect.

Abstract

We derive diffusion equations, which describe spin-charge coupled transport on the helical metal surface of a three-dimensional topological insulator. The main feature of these equations is a large magnitude of the spin-charge coupling, which leads to interesting and observable effects. In particular, we predict a new magnetoresistance effect, which manifests in a nonohmic correction to a voltage drop between a ferromagnetic spin-polarized electrode and a nonmagnetic electrode, placed on top of the helical metal. This correction is proportional to the cross-product of the spin polarization of the ferromagnetic electrode and the charge current between the two electrodes. We also demonstrate tunability of this effect by applying a gate voltage, which makes it possible to operate the proposed device as a transistor.