Tunnel Magnetoresistance scan of a pristine three-dimensional topological insulator

TL;DR

This paper proposes a three-terminal measurement setup to detect spin-momentum locking in pristine 3D topological insulators via tunnel magnetoresistance, offering a new way to analyze surface state magnetization and spin textures.

Contribution

It introduces a novel multiterminal TMR method to directly probe spin-momentum locking and out-of-plane spin polarization in 3D topological insulators, especially Bi2Te3.

Findings

Demonstrates TMR response linked to specific Fermi surface segments

Provides a method to measure momentum-resolved spin polarization

Offers a signature for spin-momentum locking in nonmagnetic TIs

Abstract

Though the Fermi surface of surface states of a 3D topological insulator (TI) has zero magnetization, an arbitrary segment of the full Fermi surface has a unique magnetic moment consistent with the type of spin-momentum locking in hand. We propose a three-terminal set up, which directly couples to the magnetization of a chosen segment of a Fermi surface hence leading to a finite tunnel magnetoresistance (TMR) response of the nonmagnetic TI surface states, when coupled to spin polarized STM probe. This multiterminal TMR not only provides a unique signature of spin-momentum locking for a pristine TI but also provides a direct measure of momentum resolved out of plane polarization of hexagonally warped Fermi surfaces relevant for $Bi_2Te_3$, which could be as comprehensive as spin-resolved ARPES. Implication of this unconventional TMR is also discussed in the broader context of 2D spin-orbit (SO) materials.