The Design And Property Research Of New Two-dimensional Topological Materials

The rapid development of miniaturization of electronic devices has approached the physical limit.It is urgent to find devices with low dissipation and high transmission.The topological properties of two-dimensional materials meet the needs of preparing low energy consumption and high density storage devices.If materials with these characteristics are applied to actual production and life to solve the heating problem caused by device miniaturization,it is very likely to break the bottleneck caused by Moore’s Law,thus promoting the development of science and technology in the new information era.Based on this,this paper studies two-dimensional new topological materials through first-principles calculation,and the research contents are as follows:First of all,we have designed a new two-dimensional topological material of honeycomb Kagome lattice:Na₃Te₂,Rb₃Sb₂.The results show that they all have intrinsic ferromagnetism,the Curie temperature of the former is 192 K,and the latter is as high as 429 K.The spontaneous magnetization of the material itself is the basis for realizing the quantum anomalous Hall effect.Their out-of-plane and in-plane magnetic anisotropy are confirmed by calculating the magneto-crystalline anisotropy energy.The spin-orbit coupling makes Na₃Te₂ open a gap of 8.2me V at the K point.The Chern number of the material is determined to be C=-1 by the Berry curvature of the k space integral.Similarly,considering spin-orbit coupling,28me V gap is opened at the dirac point.Edge state further confirmed that Na₃Te₂ and Rb₃Sb₂materials are quantum anomalous Hall effect insulators with 100%spin polarization.Moreover,it has good dynamic stability and thermal dynamic stability,high Curie temperature,and is expected to be synthesized by experimental means at room temperature.These properties show that Na₃Te₂and Rb₃Sb₂structures have broad application prospects in the preparation of low-energy spintronic materials and devices.Secondly,based on first principles calculations,a two-dimensional hexagonal honeycomb Ru CS3 thin film with a structure similar to Cr Ge Te was designed and systematically studied.The stability can be verified by the cohesive energy,phonon dispersion,molecular dynamics.The magnetic exchange mechanism could be understood by Ru-S-Ru super-exchange interactions.We’ve confirmed this by constructing and analyzing magnetic structures.And the Curie temperature is estimated to be higher than room temperature.Without the effect of SOC taken into account,the Ru CS₃film has a single-spin polarized Dirac cone structure at the point K.When considering SOC,the ferromagnetic spin arrangement perpendicular to the two-dimensional plane destroys the mirror symmetry,resulting in the degeneracy release and band gap at the K point（which naturally also belongs to theΓ-K high symmetry line）.The spin down band structure opens a global band gap about 336 me V.On this basis,the intrinsic QAH effect of Ru CS₃ have been verified by Chern number（C=1）and the chiral edge states.This result indicates its potential application in designing energy efficient spintronic devices.Finally,we designed the 2D tetragonal ZnB structure,and found that it is a very stable and anisotropic nodal-line material.The structure has good mechanical stability,dynamic stability.The results show that the nodal-line of ZnB is mainly formed by the band of p_xy orbitals of Zn and B atoms and p_z orbitals of B atoms crossing on the Fermi surface.ZnB presents a knot line ring centered on S point in BZ,which is protected by the mirror reverse symmetry and the p_xy/p_zband crossing.We further tested the robustness of the nodal ring under biaxial strain by applying up to-4%in-plane compression strain and 5%tensile strain on the ZnB monolayer respectively.The SOC causes R₁ and R₂around S point to open gaps.In order to check non-trivial topological characteristics of the ZnB film,we calculated edge states and Z₂ invariant of system.These confirm that ZnB monolayer is 2D topological insulator.In addition,we also found interesting negative differential resistance effect when studying its transmission properties.Our research has opened the way for the study of spintronics and the manufacture of new quantum devices.