Research On The Design And Topological Properties Of New 2D Materials

This article is based on the calculation of first principles,the four types of design of a 2d new nano material,and explore their topological properties,studying the two-dimensional material can achieve quantum spin hall effect and anomalous quantum hall effect,unique properties such as to promote the development of 2 d topological insulators in the experiment,in order to realize the electronic devices in the purpose of low energy consumption.Band topology and Rashba spin splitting?RSS?are two extensively explored exotic properties in condensed matter physics.However,the coexistence has rare been reported in simplest stoichiometric films so far.Here,by using first-principles calculations,we demonstrate that a series of inversion-asymmetric group-IV XYH₂ monolayers?X,Y=Si,Ge,Sn,Pb?allow for the simultaneous presence of topological order and large RSS that derives from their peculiarly atomic structure.The topological bulk gaps and RSS energies of PbSnH₂,PbGeH₂,and PbSiH₂ are tunable over a wide range of strains?-8-8%?,even the maximum value can be enhanced to 0.68 eV and 0.24 eV under achievable strain,but other three configurations transform from trivial to nontrivial phases under tensile strain.Furthermore,we find that the Te?111?-terminated BaTe surface is an ideal substrate for the growth of these monolayers,without destroying their intrinsic band topology.Our findings provide a possible route to future applications of inversion-asymmetric topological insulators in spintronic devices.The coexistence of nontrivial topology and giant Rashba splitting,however,has rare been observed in two-dimensional?2D?films,limiting severely its potential applications at room temperature.Here,we through first-principles calculations to propose a series of inversion-asymmetric group-IV films,ABZ₂?A?B=Si,Ge,Sn,Pb;Z=F,Cl,Br?,whose stability are confirmed by phonon spectrum calculations.The analyses of electronic structures reveal that they are intrinsic 2D TIs with a bulk gap as large as 0.74 eV,except for GeSiF2,SnSiCl₂,GeSiCl₂ and GeSiBr₂ monolayers which can transform from normal to topological phases under appropriate tensile strain of 4,4,5,and 4%,respectively.The nontrivial topology is identified by Z₂ topological invariant together with helical edge states,as well as the berry curvature of these systems.Another prominent intriguing feature is the giant Rashba spin splitting with a magnitude reaching 0.15 eV,the largest value reported in 2D films so far.The tunability of Rashba SOC and band topology can be realized through achievable compressive/tensile strains?-4⁶%?.Also,the BaTe semiconductor is an ideal substrate for growing ABZ₂ films without destroying their nontrivial topology.The quantum anomalous Hall?QAH?effect has attracted extensive attention due to time-reversal symmetry broken by a staggered magnetic flux emerging from ferromagnetic ordering and spin-orbit coupling.However,the experimental observations of QAH effect are still challenging due to its small nontrivial bulk gap.Here,based on density functional theory?DFT?and Berry curvature calculations,we propose the realization of intrinsic QAH effect in two-dimensional?2D?hexagonal metal-oxide lattice,Nb₂O₃,which is characterized by the nonzero Chern number?C=1?and chiral edge states.Spin-polarized calculations indicate that it exhibits Dirac half-metal feature with temperature as large as T_C=392 K using spin wave theory.When the spin-orbital coupling?SOC?is switched on,Nb₂O₃ becomes a QAH insulator.Notably,the nontrivial topology is robust against biaxial strain with its band gap reaching up to E_g=75 meV,which is far beyond the room temperature.A tight-binding?TB?model is further constructed to understand the origin of nontrivially electronic properties.Our findings on Dirac half-metal and room temperature QAH effect in the Nb₂O₃ lattice can serve as an ideal platform for developing future topotronics devices.Though quantum spin Hall effect?QSHE?in two-dimensional?2D?crystals has been widely explored,the experimental realization of quantum transport properties is only limited to HgTe/CdTe or InAs/GaSb quantum wells.Here,we employ a tight-binding model in the basis of,and_-orbitals to propose QSHE in the triangular lattice,which are driven by an crossing of electronic bands at the?point.We also propose MoS₂ as an ideal substrate for the experimental synthesis of W₂M₂C₃O₂,maintaining its nontrival topology.