Resonating-valence-bond contribution to superconductivity inMgB2

We view ${\mathrm{MgB}}_2$ as electronically equivalent to (nonstaggered) graphite $({\mathrm{B}}^{-}$ layer) that has undergone a zero-gap-semiconductor-to-superconductor phase transition by large c-axis (chemical) pressure due to ${\mathrm{Mg}}^{++}$ layers. Further, like the pπ-bonded planar organic molecules, graphite is a resonating-valence-bond (RVB) system. The RVB’s are the “preexisting Cooper pairs” in the “parental” zero-gap semiconducting ${\mathrm{B}}^{-}$ (graphite) sheets that manifest themselves as a superconducting ground state of the transformed metal. Some consequences are pointed out.