A novel carbon–nitrogen Dirac semimetal C5N4 monolayer

Two-dimensional (2D) carbon–nitrogen materials have aroused a lot of interest due to their amazing performance and possible uses. However, only a few of them have been discovered to have semimetallic properties. Based on first-principles calculations, we predict a unique 2D Dirac semimetal C5N4 with stable thermodynamics, dynamics, and mechanics. The Dirac cones in the system are rightly located at the Fermi level, and they are mostly contributed by the pz orbitals of C and N atoms. By examining the irreducible representations of related Bloch states, we discover that they are protected by the συ(x) and C2z symmetries. In addition, we establish a k⋅p model and an 18-band tight-binding (TB) model to investigate the formation and properties of Dirac points. Furthermore, we find that the Dirac points are robust to external strains. Finally, we propose a method for synthesizing this material. The C5N4 monolayer is a novel potential material for high-performance electronic devices in the future.