Based on first-principles calculations and tight-binding model analysis, we propose that black phosphorus (BP) can host a three-dimensional topological node-line semimetal state under pressure when spin-orbit coupling (SOC) is ignored. A closed topological node line exists in the first Brillouin zone (BZ) near the Fermi energy, which is protected by the coexistence of time-reversal and spatial inversion symmetry with band inversion driven by pressure. Drumhead-like surface states have been obtained on the beard (100) surface. Due to the weak intrinsic SOC of phosphorus atom, a band gap less than 10 meV is opened along the node line in the presence of SOC and the surface states are almost unaffected by SOC.
@article{arxiv.1511.05704,
title = {Topological Node-Line Semimetal in Compressed Black Phosphorus},
author = {Jianzhou Zhao and Rui Yu and Hongming Weng and Zhong Fang},
journal= {arXiv preprint arXiv:1511.05704},
year = {2016}
}