First-principles Study Of Graphene-like Two-dimensional Single-layer Materials Be₃X₂ And Other Similar Materials

The two-dimensional Dirac material has massless carriers and exhibits a special topological phase,which makes its carrier mobility extremely high;the energy band near the Fermi level is linearly dispersed,and its electron motion law can be used.The Lac equation is described.These properties will make the two-dimensional Dirac material have great potential in the field of high-performance electronics and spintronic devices.However,the Dirac core in most two-dimensional Dirac materials can only exist without spin-orbit coupling?SOC?.In the case of SOC considerations,the Dirac point will open a gap and cause topological insulation properties of the two-dimensional Dirac material.Especially when the SOC intensity is very strong,the two-dimensional topological insulator?TI?exhibits a quantum spin Hall effect with a spin-filtered edge state in its volume SOC gap.The research on Dirac materials and topological insulators has never stopped.It is a research hotspot to construct new Dirac materials and topological insulators by using structures similar to graphene.The characteristics of high-speed,low-energy spintronic devices have attracted much attention because of their great potential to replace traditional electronic devices.Conventional ferromagnetic metal spin polarization is very low at the Fermi level and can only partially provide spin-polarized carriers,which limits their practical application.The semi-metallic material has both the electronic properties of the metal and the semiconductor/insulator,and can fully provide a spin-polarized carrier,giving it a special magnetic property.This gives the semi-metal materials a broad prospect in the application of spintronic devices.Based on the above situation,in this paper,we have done the following work through first-principles calculations:?1?We designed a two-dimensional topological insulator family with HK lattice structure,namely 2D material Be₃X₂?X=C,Si,Ge,Sn?.Based on the bond-forming properties of chemical bonds and phonon dispersion relationships and molecular dynamics simulations,we confirmed their stability.By studying their electronic and topological properties,we found that the band gap is very small considering SOC,so Be₃C₂ and Be₃Si₂ are considered to be two-dimensional Dirac materials.Considering the SOC,the band gaps of Be₃Ge₂ and Be₃Sn₂ are 1.5 meV and 11.7 meV,respectively,and have a semi-infinite Dirac edge state.Therefore they belong to topological insulators.Our research will enrich the 2DTI family and promote the development of2D materials.?2?We predicted a new 2D material with a HK lattice-a single layer of Mg₃Si₂.It can be seen that it is stable by the phonon dispersion curve.The ground state of the Mg₃Si₂ material is an AFM semiconductor.By using electron or hole doping,the magnetic ground state in a single layer of Mg₃Si₂ will change from AFM to FM state,a semi-metallic material with fully spin-polarized carriers.It has been found that its semi-metallicity comes from the p_y orbital of Si and Mg atoms in the case of carrier doping.Single-layer Mg₃Si₂ has great potential applications in 2D spintronic devices with electrically controlled spin currents.