A family of robust Dirac cone materials: two-dimensional hexagonal M₃X₂ (M = Zn/Cd/Hg, X = Si/Ge)

The fascinating Dirac cone, which has produced some excellent properties in graphene, such as ballistic charge transport, ultra-high carrier mobility and the quantum Hall effect, has motivated researchers to design and study more two dimensional (2D) Dirac materials. In this work, we have designed a family of 2D Dirac cone materials M₃X₂ (M = Zn/Cd/Hg, X = Si/Ge) and studied their superior properties by first principles calculation. The calculated cohesive energy, phonon dispersion and ab initio molecular dynamics confirmed the energetic, dynamic and thermodynamic stability of Zn₃Ge₂, Cd₃Ge₂, Hg₃Si₂, and Cd₃Si₂ monolayers. It was found that the intrinsic Dirac cones exist in the electronic structure of the Zn₃Ge₂, Cd₃Ge₂, Hg₃Si₂ and Cd₃Si₂ monolayers. Their Fermi velocities are from 3.26 × 10⁵ m s^-1 to 4.32 × 10⁵ m s^-1 (8.2 × 10⁵ m s^-1 for graphene). It is noteworthy that the Dirac cone in the M₃X₂ structure is robust. It is independent of external strain (from -7% to +19%) and can also be preserved as one-dimensional zigzag nanoribbons and multilayers (from two to three-layers). Our work shows that the novel M₃X₂ Dirac cone materials are an important candidate for high-speed nanoelectronic devices.