Superconducting Proximity Effect in Graphite Films

Theoretical analysis of superconducting current in graphite films (or graphen)in proximity to superconductors is presented. In this work, the band structure of the graphite film is treated seriously: because of the delicate band structure of graphite, the actual band structure of the film, which undergoes the effects of various external factors such as leads and gates, can show a wide variety. We introduce following three models: 1) graphen-like Fermi points, 2) semi-metal, 3) electron (or hole) pockets, and 4) semiconducting gap. The superconducting critical current I{\_}c = exp {\{}- L/xi(T){\}} is studied where L is the distance between two leads and xi(T) is the coherence length in the graphite film. The temperature dependence of xi(T) is largely affected by the band structure and by examining this dependence the electronic properties of the graphite film can be estimated. The results are compared with actual experiments.