Electrical detection of the spin polarization due to charge flow in the surface state of the topological insulator Bi_1.5 Sb_0.5 Te_1.7 Se_1.3

TL;DR

This study demonstrates an all-electrical method to detect spin polarization in the surface state of a topological insulator, highlighting the importance of Fermi-level tuning for effective spin detection.

Contribution

The paper introduces a novel electrical detection technique for spin polarization in topological insulators using ferromagnetic electrodes and magnetoresistance measurements.

Findings

Spin polarization detected via magnetoresistance in BSTS

Null result in Bi2Se3 highlights Fermi-level importance

Surface state spin polarization linked to charge flow

Abstract

We detected the spin polarization due to charge flow in the spin non-degenerate surface state of a three dimensional topological insulator by means of an all-electrical method. The charge current in the bulk-insulating topological insulator Bi1.5Sb0.5Te1.7Se1.3 (BSTS) was injected/extracted through a ferromagnetic electrode made of Ni80Fe20, and an unusual current-direction-dependent magnetoresistance gives evidence for the appearance of spin polarization which leads to a spin-dependent resistance at the BSTS/Ni80Fe20 interface. In contrast, our control experiment on Bi2Se3 gave null result. These observations demonstrate the importance of the Fermi-level control for the electrical detection of the spin polarization in topological insulators.