Switching of Charge-Current-Induced Spin Polarization in the Topological Insulator BiSbTeSe2

TL;DR

This study reveals a switchable spin polarization in BiSbTeSe2 topological insulators, driven by changes in chemical potential and surface states, enabling potential spin transistor applications.

Contribution

It demonstrates the unexpected switching of spin polarization in BiSbTeSe2 due to trivial surface states, advancing understanding of spin control in topological insulators.

Findings

Spin polarization switches with chemical potential in BiSbTeSe2.

Trivial surface states with Rashba splitting cause the polarization reversal.

Potential for spin transistor operation in topological insulator devices.

Abstract

The charge-current-induced spin polarization is a key property of topological insulators for their applications in spintronics. However, topological surface states are expected to give rise to only one type of spin polarization for a given current direction, which has been a limiting factor for spin manipulations. Here we report that in devices based on the bulk-insulating topological insulator BiSbTeSe2, an unexpected switching of spin polarization was observed upon changing the chemical potential. The spin polarization expected from the topological surface states was detected in a heavily electron-doped device, whereas the opposite polarization was reproducibly observed in devices with low carrier densities. We propose that the latter type of spin polarization stems from topologically-trivial two-dimensional states with a large Rashba spin splitting, which are caused by a strong band bending at the surface of BiSbTeSe2 beneath the ferromagnetic electrode used as a spin detector. This finding paves the way for realizing the "spin transistor" operation in future topological spintronic devices.