Electronic structures and topological properties of TeSe2 monolayers

The successfully experimental fabrication of two-dimensional Te monolayer films[Phys.Rev.Lett.119106101(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 Px,Py orbitals and Te Px,Py orbitals during the process.Our work realizes topological states in the group-Ⅵmonolayers and promotes the potential applications of the materials in spintronics and quantum computations.