title: Theoretical explanation of superconductivity in C6Ca.
abstract: Using density functional theory, we demonstrate that superconductivity in C6Ca is phonon mediated with lambda = 0.83 and phonon frequency (omega)log = 24.7 meV. The calculated isotope exponents are alpha(Ca) = 0.24 and alpha(C) = 0.26. Superconductivity is due mostly to C vibrations perpendicular and Ca vibrations parallel to the graphite layers. Since the electron-phonon couplings of these modes are activated by the presence of an intercalant Fermi surface, the occurrence of superconductivity in graphite intercalated compounds requires a noncomplete ionization of the intercalant.
authors.affiliation: Institut de Minéralogie et de Physique des Milieux Condensés, 4 place Jussieu, 75252, Paris cedex 05, France.
authors.forename: Matteo
authors.initials: M
authors.lastname: Calandra
authors.forename: Francesco
authors.initials: F
authors.lastname: Mauri