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 Γˉ 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).
@article{arxiv.1608.03029,
title = {Topologically entangled Rashba-split Shockley states on the surface of grey arsenic},
author = {Peng Zhang and J. -Z. Ma and Y. Ishida and L. -X. Zhao and Q. -N. Xu and B. -Q. Lv and K. Yaji and G. -F. Chen and H. -M. Weng and X. Dai and Z. Fang and X. -Q. Chen and L. Fu and T. Qian and H. Ding and S. Shin},
journal= {arXiv preprint arXiv:1608.03029},
year = {2017}
}