Superconductivity in intercalated group-IV honeycomb structures

We present a theoretical investigation on the electron-phonon superconductivity of honeycomb MX2 layered structures where X is one element of group IV (C, Si, or Ge) and M is an alkali or an alkaline-earth metal. Among the studied compositions we predict a T-C of 7 K in RbGe2, 9 K in RbSi2, and 11 K in SrC2. All these compounds feature a strongly anisotropic superconducting gap. Our results show that despite the different doping levels and structural properties, the three families of materials fall into a similar description of their superconducting behavior. This allows us to estimate an upper critical temperature of about 20 K for the class of intercalated group-IV structures, including intercalated graphite and doped graphene.