The potential for mean-field $d$-wave superconductivity in graphite

We investigate the possibility of inducing superconductivity in a graphite layer by electronic correlation effects. We use a phenomenological microscopic Hamiltonian[1] which includes nearest neighbor hopping and an interaction term which explicitly favors nearest neighbor spin-singlets through the well-known resonance valence bond (RVB) character of planar organic molecules. Treating the Hamiltonian in mean-field theory, allowing for bond-dependent variation of the RVB order parameter, we show that both $s$- and $d$-wave superconducting states are possible with the $d$-wave state having a significantly higher $T_c$ at finite doping. By using density functional theory we show that the doping induced from sulfur absorption on a graphite layer is enough to cause an electronically driven $d$-wave superconductivity at graphite-sulfur interfaces (see e.g. [2]). We will also briefly discuss applying our results in the case of the intercalated graphites as well as the validity of a mean-field approach. \newline [1] G. Baskaran PRB {\bf 65} 212505 (2002) \newline [2] S. Moehlecke {\it et al.} PRB {\bf 69} 134519 (2004)