Theory of Multiband Superconductivity in Iron Pnictides

The precise nature of unconventional superconductivity (SC) in iron pnictides is presently a hotly debated issue. Here, using insights from normal state electronic structure and symmetry arguments, we show how an unconventional SC emerges from the bad metal normal state. Short-ranged, multiband spin and charge correlations generate nodeless SC in the active planar d(xz,yz) bands, and an interband proximity effect induces out-of-plane gap nodes in the passive d(3z)(2)-r(2) band. While very good quantitative agreement with various key observations in the SC state and reconciliation with NMR and penetration depth data in the same picture are particularly attractive features of our proposal, clinching evidence would be an experimental confirmation of c-axis nodes in future work.