Discovery of highly spin-polarized conducting surface states in the strong spin-orbit coupling semiconductor Sb$_2$Se$_3$

TL;DR

This study reveals that Sb$_2$Se$_3$, a strong spin-orbit coupling semiconductor, exhibits highly spin-polarized surface states and signs of non-trivial spin texture, suggesting it may be close to a topological insulator phase under ambient conditions.

Contribution

The paper demonstrates the presence of highly spin-polarized surface states and quasiparticle interference patterns in Sb$_2$Se$_3$, indicating potential topological properties without requiring pressure.

Findings

Generation of highly spin-polarized current in Sb$_2$Se$_3$

Observation of large negative and anisotropic magnetoresistance

Detection of quasiparticle interference patterns around defects

Abstract

Majority of the A$_2$B$_3$ type chalcogenide systems with strong spin-orbit coupling, like Bi$_2$Se$_3$, Bi$_2$Te$_3$ and Sb$_2$Te$_3$ etc., are topological insulators. One important exception is Sb$_2$Se$_3$, where a topological non-trivial phase was argued to be possible under ambient conditions, but such a phase could be detected to exist only under pressure. In this Letter, we show that like Bi$_2$Se$_3$, Sb$_2$Se$_3$, displays generation of highly spin-polarized current under mesoscopic superconducting point contacts as measured by point contact Andreev reflection spectroscopy. In addition, we observe a large negative and anisotropic magnetoresistance in Sb$_2$Se$_3$, when the field is rotated in the basal plane. However, unlike in Bi$_2$Se$_3$, in case of Sb$_2$Se$_3$ a prominent quasiparticle interference (QPI) pattern around the defects could be obtained in STM conductance imaging. Thus, our experiments indicate that Sb$_2$Se$_3$ is a regular band insulator under ambient conditions, but due to it's high spin-orbit coupling, non-trivial spin-texture exists on the surface and the system could be on the verge of a topological insulator phase.