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.