Phase polymorphism and electronic structures of TeSe2

Abstract

Structure prediction complemented by density functional theory (DFT) calculation indicates that TeSe₂ is the most stable among the various Te_(1−x)Se_x compounds. Different from the case of bulk Te, the material can equally adopt three different crystal structures: H_γT, M_H, and M_βα phases, which are similar to 1T-TiSe₂, trigonal Te, and orthorhombic Te, respectively. These phases can be transformed from one to another by uniaxial tensile and shear stress of less than 1 MPa; they can be even transformed to their chiral mirror images. Band structure calculations including spin–orbit coupling (SOC) show that all three phases are semiconductors. The band gap (= 0.43 eV) increases with density, being the largest (= 1.86 eV) in the M_βα phase with the highest density. The H_γT phase exhibits a hidden spin texture because of centrosymmetry. The other two phases display chiral spin texture due to the lack of symmetry, in that two spin components of frontier bands can split by more than 100 meV in opposite directions.