Superconducting proximity effect through graphene and graphite films

Abstract

We discuss the superconducting proximity effect in graphite films (or graphene) by studying the critical current through superconductor-graphite film (or graphene)-superconductor Josephson junction. The two leads are assumed to be conventional s-wave superconductors. We especially pay attention to the dispersions of electrons in graphite films: because of the delicate band structure of graphite, the electron dispersion in the film, which undergoes the effects of various external factors such as leads, gate electrodes and sample inhomogeneities, can show a wide variety. We introduce several models for electron dispersion near Fermi energy: 1) graphene-like Fermi points, 2) semi-metal, and 3) semiconducting gap. The superconducting critical current Ic through the junction is usually expressed as Ic α exp(-d/ξ(T)}, where d is the distance between two leads and ξ(T) is the proximity length. We show that the temperature dependence of ξ(T) is largely affected by the band structure of the graphite film and by examining this dependence some insight into the electronic properties of the graphite film can be obtained.