Spin-orbitronics at a topological insulator-semiconductor interface

TL;DR

This study demonstrates the integration of a topological insulator with germanium to enable efficient spin detection, revealing a sign reversal in spin-to-charge conversion due to surface state hybridization, thus advancing TI-semiconductor spintronics.

Contribution

It introduces a Ge substrate for Bi₂Se₃ growth and investigates spin-to-charge conversion at their interface, revealing sign reversal and compatibility with semiconductor technology.

Findings

Reversal of spin-to-charge conversion sign in TI/Ge compared to Pt

Comparable efficiency of spin detection in TI/Ge and Pt

Hybridization explains the sign reversal via first-principles calculations

Abstract

Topological insulators (TIs) hold great promises for new spin-related phenomena and applications thanks to the spin texture of their surface states. However, a versatile platform allowing for the exploitation of these assets is still lacking due to the difficult integration of these materials with the mainstream Si-based technology. Here, we exploit germanium as a substrate for the growth of Bi$_2$Se$_3$, a prototypical TI. We probe the spin properties of the Bi$_2$Se$_3$/Ge pristine interface by investigating the spin-to-charge conversion taking place in the interface states by means of a non-local detection method. The spin population is generated by optical orientation in Ge, and diffuses towards the Bi$_2$Se$_3$ which acts as a spin detector. We compare the spin-to-charge conversion in Bi$_2$Se$_3$/Ge with the one taking place in Pt in the same experimental conditions. Notably, the sign of the spin-to-charge conversion given by the TI detector is reversed compared to the Pt one, while the efficiency is comparable. By exploiting first-principles calculations, we ascribe the sign reversal to the hybridization of the topological surface states of Bi$_2$Se$_3$ with the Ge bands. These results pave the way for the implementation of highly efficient spin detection in TI-based architectures compatible with semiconductor-based platforms.