Towards the understanding of the origin of charge-current-induced spin voltage signals in the topological insulator Bi$_2$Se$_3$

TL;DR

This study investigates the origin of voltage signals in Bi$_2$Se$_3$ topological insulators, revealing that fringe-field-induced Hall voltages, rather than spin-momentum locking, can produce similar signals, impacting spintronic device design.

Contribution

The paper demonstrates that measured voltages in Bi$_2$Se$_3$ are primarily due to fringe-field effects, challenging the assumption that they solely indicate spin-momentum locking.

Findings

Voltage reversal with magnetization inversion

Voltage dependence on bias and temperature

Fringe-field-induced Hall voltages explain signals

Abstract

Topological insulators provide a new platform for spintronics due to the spin texture of the surface states that are topologically robust against elastic backscattering. Here, we report on an investigation of the measured voltage obtained from efforts to electrically probe spin-momentum locking in the topological insulator Bi$_2$Se$_3$ using ferromagnetic contacts. Upon inverting the magnetization of the ferromagnetic contacts, we find a reversal of the measured voltage. Extensive analysis of the bias and temperature dependence of this voltage was done, considering the orientation of the magnetization relative to the current. Our findings indicate that the measured voltage can arise due to fringe-field-induced Hall voltages, different from current-induced spin polarization of the surface state charge carriers, as reported recently. Understanding the nontrivial origin of the measured voltage is important for realizing spintronic devices with topological insulators.