Massless Dirac fermions in stable two-dimensional carbon-arsenic monolayer

We predict from density functional theory based electronic structure calculations that a monolayer made up of carbon and arsenic atoms with a chemical composition $({\mathrm{CAs}}₃)$ forms an energetically and dynamically stable system in two geometrical arrangements, namely, buckled and puckered configurations. The results of electronic structure calculations predict that the puckered monolayer is a metal, whereas the buckled monolayer is a semimetal. Interestingly, the electronic band structure of the buckled configuration possesses a linear dispersion and a Dirac cone at the Fermi level around the high-symmety $K$ point in the reciprocal lattice. Thus, at low-energy excitation (up to 105 meV), the charge carriers in this system behave as massless Dirac fermions. Detailed analysis of partial density of state indicates that the $2{p}_z$ orbital of C atoms contributes significantly to the states which form the linear dispersion and hence the Dirac cone around the Fermi level. This suggests the existence of a strong correlation between the linear dispersion (Dirac cone) and ${sp}²$-like hybridization of the orbitals of C atom. Thus the electronic properties of ${\mathrm{CAs}}₃$ monolayer are similar to those of graphene and other group-IV based monolayers like, silicene and germanene. In addition, we have also investigated the influence of mechanical strain on the properties of ${\mathrm{CAs}}₃$ monolayer. Our results indicate that the monolayer possesses linear dispersion in the electronic band structure for a wide range of mechanical strain from $\ensuremath{-}12$% to 20%, though the position of Dirac point may not lie exactly at the Fermi level. Finally, we wish to point out that ${\mathrm{CAs}}₃$ monolayer belongs to the class of Dirac materials where the behavior of particles, at low-energy excitations, is characterized by the Dirac-like Hamiltonian rather than the Schrodinger Hamiltonian.