Resonating valence bonds and mean-field d -wave superconductivity in graphite

作者：Annica M. Black‐Schaffer, Sebastian Doniach · 发表于：Physical Review B · 年份：2007 · DOI：10.1103/physrevb.75.134512 · 被引用次数：267 · 研究领域：Graphene research and applications、Graphite, nuclear technology, radiation studies、Boron and Carbon Nanomaterials Research

We investigate the possibility of inducing superconductivity in a graphite layer by electronic correlation effects. We use a phenomenological microscopic Hamiltonian 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 this 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. The $d$-wave solution belongs to a two-dimensional representation and breaks time-reversal symmetry. At zero doping there exists a quantum critical point at the dimensionless coupling $J∕t=1.91$ and the $s$- and $d$-wave solutions are degenerate for low temperatures. At finite doping the $d$-wave solution has a significantly higher ${T}_{c}$ than the $s$-wave solution. 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. We also discuss applying our results to the case of the intercalated graphites, as well as the validity of a mean-field approach.