SUPERCONDUCTIVITY IN GRAPHITE-INTERCALATION COMPOUNDS

Alkali-metal graphite intercalation compounds undergo a normal-to-superconducting transition at a critical temperature T(c) that increases with increasing alkali-metal concentration. Furthermore, the temperature dependence of the critical magnetic field H(c2) is linear down to very low temperatures. A two-band model, which considers coupling between a three-dimensional band and an almost two-dimensional electronic energy band, and which was successfully applied to explain superconductivity in C8K, is used to interpret recently reported data. In particular, we show that the increase in T(c) as the alkali-metal concentration increases, the linear temperature dependence of H(c2), and the anisotropy in its value, are consistent with the two-band model.