Planar MN${}_4$ (M = Zn, Cd) monolayers. 2D anisotropic Dirac semimetals of ultrahigh Fermi velocities

After the exfoliation of graphene, it is appealing to seek more 2D Dirac materials with unique structures, rich physics, and intriguing properties. Herein, by means of density functional theory (DFT) computations, two planar 2D Dirac transition-metal nitrides are reported, namely, MN${}_4$ (M = Zn, Cd) monolayers. The basal planes of these monolayers can be regarded as tiled by hexagons and pentagons, with tetracoordinated metal and tricoordinated nitrogen as vertices. Besides the demonstrated mechanical, dynamic, and thermal stabilities, the two MN${}_4$ monolayers both exhibit an anisotropic Dirac cone at the Fermi level, thus featuring anisotropic Dirac fermions. Particularly, these Dirac fermions present ultrahigh Fermi velocities, which are in the same order of magnitude as that of graphene (10${}^6$ m s${}^{-1}$). Moreover, the Dirac cone is robust against external strains and electric fields due to the protection of σ${}_{v\left(x\right)}$ and C${}_{2z}$ symmetry. Above all, the remarkable electronic properties suggest that MN${}_4$ (M = Zn, Cd) monolayers have potential applications as nanoelectronic devices. (© 2022 Wiley‐VCH GmbH)