A Novel SiO Monolayer with Negative Poisson's Ratio and Dirac Semimetal

Although a number of interesting physical properties such as negative Poisson's ratio (NPR) and Dirac semimetal (DS) have been recently predicted in Two-dimensional (2D) materials, it has been rare to realize a 2D material that could integrate these DS and NPR features. Here adopting particle swarm optimization (PSO) algorithms combined with first-principles methods, we had successfully predicted three novel SiO monolayers (Pmna, P2221, and P2), whose dynamical and thermal stabilities were characterized by phonon spectrum and molecular dynamics simulations. In particular, Young’s modulus and Poisson’s ratio calculations find that Pmna monolayer exhibits a highly emerged mechanical anisotropy with in-plane NPR originating from its puckered atom-arrangement. More notably, the band structure of Pmna monolayer possesses zero-bandgap with four Dirac cones in its first Brillouin zone, exhibiting a DS feature. By calculations of orbit-resolved band structure, the Dirac cone was revealed to originate from the orbital hybridization of Si and O atoms. The Pmna monolayer is the first 2D structure in the Si-O system that has both NPR and Dirac semi-metal properties, providing a new model for exploring 2D multifunctional materials.