Topologically entangled Rashba-split Shockley states on the surface of grey arsenic

TL;DR

This study identifies topologically non-trivial Shockley surface states on grey arsenic (111), characterized by spin polarization and a crossing that is protected by topology, confirmed through ARPES experiments and first-principles calculations.

Contribution

It demonstrates the existence of topologically protected Shockley states on grey arsenic, combining experimental ARPES data with theoretical calculations to reveal their non-trivial topology.

Findings

Spin-polarized surface bands observed on As(111)

Surface states traverse the bulk band gap

States are of Shockley type due to band inversion

Abstract

We discover a pair of spin-polarized surface bands on the (111) face of grey arsenic by using angle-resolved photoemission spectroscopy (ARPES). In the occupied side, the pair resembles typical nearly-free-electron Shockley states observed on noble-metal surfaces. However, pump-probe ARPES reveals that the spin-polarized pair traverses the bulk band gap and that the crossing of the pair at $\bar\Gamma$ is topologically unavoidable. First-principles calculations well reproduce the bands and their non-trivial topology; the calculations also support that the surface states are of Shockley type because they arise from a band inversion caused by crystal field. The results provide compelling evidence that topological Shockley states are realized on As(111).