Monolayer Honeycomb CuSe: A Candidate for Two–dimensional Dirac Nodal Line Fermions*

Symmetry-protected Dirac nodal line semimetals (DNLSs) receive much attention because of their exotic physical properties and potential applications in dissipationless spin devices. DNLFs in 2D atomic crystal have rarely been explored because of their high vulnerability to symmetry breaking. Here we propose that free-standing monolayer CuSe with honeycomb structure is endowed with the exotic 2D DNLF protected by mirror reflection symmetry, based on first-principles calculation. The DNLF state is evidenced by nontrivial edge states that arise as the crossing bands open the gaps with spin-orbit coupling. The angle resolved photoemission spectroscopy on the as-prepared monolayer CuSe on a Cu(111) show excellent agreement with the calculated band structures of CuSe/Cu(111), which demonstrates that it is a monolayer CuSe with a distorted honeycomb lattice.

In collaboration with Lei Gao, Jia-Tao Sun, Jian-Chen Lu, Hang Li, Kai Qian, Shuai Zhang, Tian Qian, Hong Ding and Hong-Jun Gao from the Institute of Physics, CAS; X. Lin and Y. Y. Zhang from the University of CAS.