First-principles Study Of The Topological And Rashba Spin Splitting Properties In Topological Insulators

Spintronic materials have attracted great attention because of their excellent physical properties and great application.With the increasing requirements of device miniaturization and integration,exploring and regulating the spin properties of two-dimensional materials has become one of the hotspots of current research.With the rise and rapid development of topological insulators,it is found that it is possible to use electric field to regulate electrons in topological materials with strong spin orbit coupling interaction,and Rashba type spin orbit coupling in two-dimensional materials without spatial inversion symmetry has great potential application in realizing spintronic devices without external magnetic field.Therefore,using the first principle calculation method,we have carried out systematic works in exploring and regulating the spin properties of materials with spin orbit coupling interaction.The main work contents are as follows:1)Huge magneto-induced bandgaps and Rashba spin orbit coupling splitting in semi-hydrogenated graphene/Bi₂Se₃heterojunction.We constructed a heterojunction by combining the two-dimensional ferromagnetic insulator semi-hydrogenated graphene with the 3QL and 5QL of the three-dimensional topological insulator film Bi₂Se₃,respectively.Due to the C-Se atomic bond,the entire system only has a magnetic moment of 1μ_B.And it is this residual 1μB magnetic moment that breaks the time-reversal symmetry of the system,which induces huge magneto-induced band gaps of 40me V and 150me V on the topological surface states of 3QL and 5QL,respectively.In addition,due to the breaking of the spatial inversion symmetry of the system,up to 0.75 e V?Rashba spin splitting occurs in the system near the Fermi surface,and by reducing the total magnetic moment of the system to 0,the Rashba spin splitting phenomenon in the heterojunction has been significantly weakened.Therefore,our calculation results prove that magnetism has a great influence on the Rashba spin-splitting phenomenon.2)Two dimensional topological insulator with large band gap and Rashba spin splitting.Through the thermodynamic and dynamic stability test of two-dimensional o-ptl crystal,we predict a two-dimensional O-PTl crystal structure that can exist stably at 300K at room temperature.Its electronic structure has a very large 403 me V nontrivial topological band gap on the Fermi plane,and the band gap can be further expanded to 460 me V through biaxial strain.In addition,we also note that there is a giant Rashba spin orbit coupling splitting of 1.736 e V?in its eigenstate.The combination of this phenomenon and the previous two-dimensional topological insulator properties not only provides an important platform for the laboratory to realize QSHE at room temperature,but also greatly widens the application range of this material in spintronic devices.3)Giant Rashba spin splitting in Sb/X/Sb（X=Bi₂Se₃,Sb₂Te₃）.Through the construction of Sb/X/Sb（X=Bi₂Se₃,Sb₂Te₃）sandwich heterojunction.We found that due to the lack of space inversion symmetry in the heterojunction,the energy bands of the four different stacking modes（ABA,ABC,CBC and CBA）have different degrees of Rashba spins in their valence and conduction bands at Fermi planes.It is worth noting that the Rashba spin splitting value of the Sb/Bi₂Se₃/Sb heterojunction in the CBC and CBA stacking modes has reached more than 4 e V?,and the splitting value at the top of the valence band of the Sb/Bi₂Se₃/Sb heterojunction in the CBA stacking mode reaches 5.2 e V?,which is far beyond the current splitting value that has been achieved by constructing heterojunctions using experimentally prepared materials.