Graphene-like Be3X2(X=C,Si, Ge,Sn):A new family of two-dimensional topological insulators

Using first-principle calculations, we predict a new family of stable two-dimensional(2 D) topological insulators(TI),monolayer Be3X2(X = C,Si, Ge, Sn) with honeycomb Kagome lattice. Based on the configuration of Be3C2, which has been reported to be a 2 D Dirac material, we construct the other three 2 D materials and confirm their stability according to their chemical bonding properties and phonon-dispersion relationships. Because of their tiny spin-orbit coupling(SOC)gaps, Be3C2and Be3Si2are 2 D Dirac materials with high Fermi velocity at the same order of magnitude as that of graphene.For Be3 Ge2 and Be3Sn2,the SOC gaps are 1.5 meV and 11.7 meV, and their topological nontrivial properties are also confirmed by their semi-infinite Dirac edge states. Our findings not only extend the family of 2 D Dirac materials, but also open an avenue to track new 2 DTI.