Square transition-metal carbides MC₆ (M = Mo, W) as stable two-dimensional Dirac cone materials

Searching for new two-dimensional (2D) Dirac cone materials has been popular since the exfoliation of graphene. Herein, based on density functional theory, we predict a novel family of 2D Dirac cone materials in square transition-metal carbides MC₆ (M = Mo, W) which show inherent stability confirmed by phonon spectrum analysis and ab initio molecular dynamics calculations. The Dirac point, located exactly at the Fermi level, mainly arises from the hybridization of M-d_z and C-p_z orbitals which gives rise to an ultrahigh Fermi velocity comparable to that of graphene. Moreover, strong spin-orbit coupling related to M-d electrons can generate large band gaps of 35 and 89 meV for MoC₆ and WC₆ monolayers, respectively, which allows MC₆ materials to be operable at room temperature (26 meV), as candidates for nanoelectronics in the upcoming post-silicon era. The conceived novel stable metal-carbon framework materials provide a platform for designing 2D Dirac cone materials.