Study On First Principles Of New Two-dimensional Dirac Materials

Based on first-principles,this thesis studies three new types of two-dimensional?2D?materials.The main idea is to explore the quantum properties of structures by analyzing geometric structures and electronic properties.The research facilitates the further development of two-dimensional Dirac materials and will provide a new platform for new high-speed and low-dissipation devices.Firstly,we studied the two-dimensional organic structure MnCN,and we found that it is a Dirac Nodal-Line semimetal?DNL?material with spin polarization characteristics.The DNL material with spin polarization has many strange properties,which also attracted wide attention of researchers.However,the structures with DNL properties are infrequent in two-dimensional materials and are difficult to achieve experimentally.Through calculation,we found that the two-dimensional organic lattice MnCN structure is a new kind of single spin DNL material.Due to the spontaneous magnetization of the material,the two spin channels are completely separated,the spin-down channel shows a semiconducting behavior with a gap of 0.94 eV,while the spin-up one has partially filled metallic bands,showing a full spin-polarization.In order to testify the DNL properties of the material,we calculated the three-dimensional energy band of the material using the Wannier.The results show that without the spin-orbit coupling?SOC?,the MnCN structure is a spin-polarized DNL material caused by the inversion of p_x,y/p_z orbital components.This work opens up a new way to realize spin-polarized node ring materials,and is expected to be widely used in spintronic devices.Next,we study the Ta₂S₃ structure of two-dimensional Dirac films.The Ta₂S₃ monolayer exhibits dynamic and thermodynamic stability at high temperatures.More importantly,we predict a new class of single spin Dirac fermion states in the Ta₂S₃ monolayer,which is also characterized by 100%spin polarizability.Its carrier mobility can be compared with that of graphene.When the SOC is considered,the Ta₂S₃ monomer becomes a QAH insulator that does not require external magnetic field or extra magnetic doping.Finally,in order to explore the source of QAH effect,we built a TB model.These results indicate that the Ta2S3 lattice has a great prospect in the field of spintronic devices.Finally,we designed a two-dimensional B6O film with good mechanical stability and dynamic stability,and found that it was an elliptic DNL half-metal protected by symmetry.The Fermi velocity was calculated to be 10⁶ m/s,the same order of magnitude as graphene.In order to observe the energy band in the momentum space more intuitively,Wannier was used to calculate the 3D energy band of the material.Furthermore,we developed a TB model to explain the origin of DNL.Finally,we preserve the DNL fermion properties of B6O when it is placed on the h-BN substrate.These results show that the B₆O monolayer is a new platform to realize the new high speed and low dissipation devices.