Origin and evolution of surface spin current in topological insulators

TL;DR

This paper investigates how controlling bulk and surface contributions in topological insulators enhances surface spin currents, with implications for room-temperature spintronic devices.

Contribution

It demonstrates the importance of surface-dominated spin polarization and bulk conductivity suppression for efficient charge-to-spin conversion in topological insulators.

Findings

Surface spin polarization is enhanced when bulk conductivity is suppressed.

Spin signals decrease with temperature due to bulk carrier excitation and electron-phonon interactions.

Surface states maintain dominance up to room temperature, promising for spintronics.

Abstract

The Dirac surface states of topological insulators offer a unique possibility for creating spin polarized charge currents due to the spin-momentum locking. Here we demonstrate that the control over the bulk and surface contribution is crucial to maximize the charge-to-spin conversion efficiency. We observe an enhancement of the spin signal due to surface-dominated spin polarization while freezing out the bulk conductivity in semiconducting Bi1.5Sb0.5Te1.7Se1.3 below 100K. Detailed measurements up to room temperature exhibit a strong reduction of the magnetoresistance signal between 2 and 100K, which we attribute to the thermal excitation of bulk carriers and to the electron-phonon coupling in the surface states. The presence and dominance of this effect up to room temperature is promising for spintronic science and technology.