First-principles Study Of The Electronic Structure And Topological Properties Of Two-dimensional Chalcogenide Topological Insulators

Since the discovery of graphene,the research on two-dimensional materials has become more and more extensive,and the research on two-dimensional transition metal sulfides has also attracted much attention.In this thesis,a two-dimensional transition metal sulfide with two-sided asymmetry is constructed based on the Janus structure,and a class of two-dimensional transition metals with a quadrilateral-hexagon-octagon(square-hexagon-octagon,sho)structure are studied.The material properties of sulfide sho MXY(M=Mo,W;X,Y=S,Se,Te;X≠Y)are explored to explore its electronic structure,topological characteristics and carrier transport properties,and by applying double Axial strain studies the material’s response to strain-induced changes in electronic and topological properties.The results show that the Janus structure of S-Se presents semiconductor characteristics,while the Janus structure of S-Te presents metal characteristics,and will show local topological properties with the participation of different transition metal elements,and then in Se-Te The emergence of topological states is observed in the Janus structure of,and different electronic property changes appear with the different influences of transition metal ions.In addition,we further studied the influence of the Janus structure on the electronic properties and topological properties of this sho structure,and selected three structural combinations of the oxygen atom Janus structure(S-O,Se-O,Te-O)for related properties To understand the different mechanism changes of various chalcogen elements participating in the Janus structure,and to obtain a more ideal topological state in the sho Mo Se O structure,and to study its topological properties in detail.Next,we also studied the change of electronic properties of various Janus materials by applying biaxial strain.We summarized the change characteristics of different Janus structures on the strain and observed the change of their topological properties.Finally,we calculated the carrier mobility and effective mass anisotropy of several Janus structures to understand their transport properties,which provides a reference for the research of this type of Janus structure materials.