Origin of Dirac Cones in SiC Silagraphene: A Combined Density Functional and Tight-Binding Study

The formation of Dirac cones in electronic band structures via isomorphous transformation is demonstrated in 2D planar SiC sheets. Our combined density functional and tight-binding calculations show that 2D SiC featuring C-C and Si-Si atom pairs possesses Dirac cones (DCs), whereas an alternative arrangement of C and Si leads to a finite band gap. The origin of Dirac points is attributed to bare interactions between Si-Si bonding states (valence bands, VBs) and C-C antibonding states (conduction bands, CBs), while the VB-CB coupling opens up band gaps elsewhere. A mechanism of atom pair coupling is proposed, and the conditions required for DC formation are discussed, enabling one to design a class of 2D binary Dirac fermion systems on the basis of DF calculations solely for pure and alternative binary structures.