Surface band structure of $\text{Bi}_{1-x}\text{Sb}_{x}$(111)

TL;DR

This study uses ARPES to investigate the surface band structure of Bi-Sb alloys, clarifying the number of topological surface bands and resolving previous experimental-theoretical discrepancies.

Contribution

It provides experimental ARPES data showing two surface bands in Bi-Sb alloys, aligning with theoretical predictions and addressing prior controversies.

Findings

Surface band structure evolves with Sb concentration.

ARPEs data confirms two topological surface bands.

Better agreement with theoretical models.

Abstract

Theoretical and experimental studies agree that $\text{Bi}_{1-x}\text{Sb}_{x}$ ($0.07 \leq x \leq 0.21$) to be a three-dimensional topological insulator. However, there is still a debate on the corresponding $\text{Bi}_{1-x}\text{Sb}_{x}$(111) surface band structure. While three spin polarized bands have been claimed experimentally, theoretically, only two surface bands appear, with the third band being attributed to surface imperfections. Here, we address this controversy using angle-resolved photoemission spectroscopy (ARPES) on $\text{Bi}_{1-x}\text{Sb}_{x}$ films. To minimize surface imperfections, we have optimized the sample growth recipe. We have measured the evolution of the surface band structure of $\text{Bi}_{1-x}\text{Sb}_{x}$ with $x$ increasing gradually from $x = 0$ to $x = 0.6$. Our ARPES data show better agreement with the theoretical calculations, where the system is topologically non-trivial with two surface bands.