Electronic structures and topological properties of TeSe2 monolayers* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11574051 and 11874117) and Natural Science Foundation of Shanghai, China (Grant No. 21ZR1408200).

Abstract

The successfully experimental fabrication of two-dimensional Te monolayer films [Phys. Rev. Lett. 119 106101 (2017)] has promoted the researches on the group-VI monolayer materials. In this work, the electronic structures and topological properties of a group-VI binary compound of TeSe2 monolayers are studied based on the density functional theory and Wannier function method. Three types of structures, namely, α-TeSe2, β-TeSe2, and γ-TeSe2, are proposed for the TeSe2 monolayer among which the α-TeSe2 is found being the most stable. All the three structures are semiconductors with indirect band gaps. Very interestingly, the γ-TeSe2 monolayer becomes a quantum spin Hall (QSH) insulator with a global nontrivial energy gap of 0.14 eV when a 3.5% compressive strain is applied. The opening of the global band gap is understood by the competition between the decrease of the local band dispersion and the weakening of the interactions between the Se p x , p y orbitals and Te p x , p y orbitals during the process. Our work realizes topological states in the group-VI monolayers and promotes the potential applications of the materials in spintronics and quantum computations.