Superconductivity in Ca-intercalated bilayer graphene

Recent observation of proximity effect [H.B. Heersche, P. Jarillo-Herrero, J.B. Oostinga, L.M.K. Vandersypen, and A.F. Morpurgo, Nature, bf 446 (2007) p. 05555.] has ignited interest in superconductivity in graphene and its derivatives. We consider Ca-intercalated graphene bilayer and argue that it is a superconductor, and likely with a sizeable T _c . We find substantial and suggestive similarities between Ca-intercalated bilayer (C₆CaC₆), and CaC₆, an established superconductor with T _c = 11.5 K. In particular, the nearly free electron band, proven to be instrumental for superconductivity in intercalated graphites, does cross the chemical potential in (C₆CaC₆), despite the twice smaller doping level, satisfying the so-called “Cambridge criterion”. Calculated properties of zone-center phonons are very similar to those of CaC₆. This suggests that the critical temperature would probably be on the same scale as in CaC₆.