Structure Design Of Quantum Spin Hall Insulators And Manipulation Of Topological Surface States

There are a lot of peculiar properties in the topological insulators?TIs?.These properties have many potential applications in spin electronics and topological quantum computation.There is a surface state or boundary state on the topological insulators.In their bulks,the materials are insulated.however,the surface of the materials is conductive,showing metal States.The electronic spin and angular momentum on the surface are perpendicularly locked,which is protected by time-inversion symmetry.TIs has a lot of application value in fabricating new quantum devices.Because its spin and charge currents could transport without dissipation.In the first chapter,the thesis mainly introduces the hall effect,the quantum spin hall.The research progress and theoretical knowledge of the three-dimensional Topological insulators are also introduced in this chapter.In the second chapter,the thesis introduces the density functional theory,Theoretical derivation process of phonon spectrum and the Vienna ab initio simulation package?VASP?.In the chapter three,the thesis introduces the research results of quantum spin hall effect.It is very important to find quantum spin hall insulators which are stable and have large gap.According to first-principles calculations,metallic As?110?and Sb?110?bilayers become QSH insulators after chemically functionalized using hydrogen?H?or halogen?Cl and Br?atoms.The energy gaps of the functionalized films range from 0.121 to 0.304 eV,which is enough for room temperature applications.The energy gaps mainly origin from the spin-orbit coupling?SOC?.And as SOC strength??/?₀?grows up,the energy gap almost increases linearly.The penetration depth of edge states of all these X-D films is about 1 nm.Z₂ topological invariants are also calculated,which confirms these X-D films are quantum spin Hall insulators further.In the chapter four,the thesis introduces the magnetic control of magnetic elements on the surface state of the Topological insulators.In order to realize Topological magnetoelectric effect,we need to introduce the time inversion symmetry to open the gap of Dirac cone.We replace Pb of Pb₂Bi₂Se₅ with magnetic elements?Mn Eu?.Then we Combine X₂Bi₂Se₅ with Bi₂Se₃ to construct the heterojunction.Based on the first-principle calculations,we find that X₂Bi₂Se₅ all are AFM?,whose energy gap are large.The energy gaps of Mn₂Bi₂Se₅ and Eu₂Bi₂Se₅ are that 0.249eV and 0.189eV respectively.the band structure indicates that the energy gaps of X₂Bi₂Se₅ Bi₂Se₃ are opened.The energy gap of Mn₂Bi₂Se₅ Bi₂Se₃ is opened to 0.016eV.And the energy gap of Eu₂Bi₂Se₅ Bi₂Se₃ is opened to 0.012eV.