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Abstract
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.
Acknowledgements
We are grateful to I. Lukyanchuk and T. Wehling for useful discussions. This work was supported by US DoE BES and LDRD at Los Alamos.
Notes
Notes
1. Recent measurements of the Ca isotope effect suggest that the Ca contribution may be even higher.
2. One can deposit the Ca atoms on the single graphene sheet. However in this case effect of top Ca atoms will be very different and one would need a detail characterization of a substrate.
3. It might also be possible to cover bilayer graphene with Ca, adding carriers and likely improving superconducting properties, but the phonon properties of a Ca overlayer will be very different from that of intercalated Ca and are beyond the scope of this article.