Theoretical Study On Topological Electronic Properties Of Layer Transition Metal Chalcogenides

In condensed matter physics,where one is interested in 2D layered materials due to their rich and unique properties and broad application.Low-dimensional materials mainly include graphene,black phosphorus,silicon,Bi₂Se₃,transition metal dichalcogenides?TMDs?and single-layer Fe Se,etc.,which exhibit some new quantum phenomena,such as valley-type spintronics,topological insulator,quantum Hall effect,topological semimetal?SM?and superconductivity.These quantum phenomena have great application value in micro-nano energy electronic equipment,optoelectronic equipment and topological quantum computing.TMDs not only have high application value in the fields of electronics,optics,machinery,chemistry and catalysis,but also have potential research value in topological materials.With the development of SM materials,more and more topological materials have been discovered.But the ideal topology materials are still lacking.Therefore,searching for new topological SM and effectively modulating the discovered Weyl SM have become the main methods to obtain ideal SM.In this paper,we first provided two new candidate materials which are transition metal monochalcogendes?TMM?possessing non-centrosymmetric crystal structure:MTe?M=W,Mo?and W₂XY?X,Y=S,Se,Te,X?Y?,modulated the topological electronic properties of T_d-Mo Te₂ and explored the electronic properties of the twisted2H-Mo Te₂.We first proved that the Mo Te and WTe are both novel Dirac-Weyl semimetals with Weyl and Dirac fermions.Afterwards we confirmed that W₂XY are novel topology SM with Type I and Type II Weyl points.In addition,we modulate the topological properties of T_d-Mo Te₂ by alloying and strain.The main results show that substitutional disordered alloy Mo Te_2-xS_x?x=0.25?replacing different positions will result in a different number of Weyl points?WP?,and the minimal number WP in a time-reversal symmetry Weyl SM is obtained in one alloying system.The WP's energy of the alloying system are closer to the Fermi level after shear strain.Finally,the electronic properties of twisted 2H-Mo Te₂ was performed.The main result showed that the twisting caused an indirect band gap to a direct band gap,and the band gap first increased and then decreased with the increase of the twist angle.Our research results have expanded the understanding of topological SM and provided the measure to obtain"ideal"topological materials.And provided the theoretical basis for the practical application of TMDs in topological electronic devices,energy and quantum computing.