Superconductivity in Ca-intercalated bilayer graphene

摘要

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 (C_6CaC_6), and CaC_6, 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 chemicalpotential in (C_6CaC_6), despite the twice smaller doping level, satisfying the so-called ‘‘Cambridge criterion’’. Calculated properties of zone-center phonons are very similar to those of CaC_6. This suggests that the critical temperature would probably be on the same scale as in CaC_6.