First Principles Study Of Transition Metal Chalcogenide Layered Materials

In recent years,two-dimensional materials have attracted much attention due to their novel and unique properties and broad application prospects.In addition to the earliest discovered graphene,the layered transition metal chalcogenide material has great potential in many fields due to its excellent physical properties.The main content of this dissertation is the regulation effect of magnetic proximity effect on monolayer Mo S₂ valley splitting and the modification of the bilayer WSe₂ electronic structure by the banding engineering of the doping method.The main research results of this dissertation are shown below.The valleytronic property in monolayer Mo S₂ induced by the magnetic proximity effect of a robust type-II antiferromagnetic insulating Co O at room temperature as the magnetic substrate has been investigated by using first principles calculations and the maximally localized Wannier function method.The results show that monolayer Mo S₂ can achieve 103me V large valley splitting when coupled to an antiferromagnetic insulating Co O(111)substrate.The substrate provides a 152 T Zeeman field,and breaking of the time-reversal symmetry of monolayer Mo S₂ leads to a prominent anomalous Hall conductivity,particularly that has quantized character in the range of the band edge at the K and K'valleys.Based on the result that the valley-contrasting Berry curvature is opposite at the K and K'valleys,a valleytronic device that can be used as a filter for both the valley and spin is proposed.The structural,electronic and magnetic properties of Cr,Mn,Fe,Co and Ni-doped bilayer WSe₂ are predicted by using first principles calculations.The doped transition-metal atoms show a covalent-binding with the nearest Se atoms.The calculated electronic structures reveal that the transition metal Cr,Mn,Fe and Co-doped bilayer WSe₂ exhibit the half-metallic character with a 100%spin polarization at the Fermi level,and the reason is ascribed to the strong hybridization peak between the transition metals and parent W and Se atoms.The Fe-doped system has a robust stability of half-metallicity because there are three connected states peak spanning the Fermi level.The predicted Cr,Mn,Fe and Co-doped bilayer WSe₂ should be the candidate materials for spintronic device due to their magnetic and half-metallic nature.