Theory of Multiband Superconductivity in Iron Pnictides

TL;DR

This paper presents a theoretical framework explaining how unconventional multiband superconductivity arises in Iron Pnictides from their electronic structure and correlations, predicting nodeless gaps in active bands and nodes in passive bands.

Contribution

It introduces a novel theory linking normal state electronic correlations to the emergence of multiband superconductivity with specific gap structures in Iron Pnictides.

Findings

Quantitative agreement with experimental observations

Prediction of c-axis nodes in passive bands

Explanation of nodeless gaps in active bands

Abstract

The precise nature of unconventional superconductivity 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, multi-band spin- and charge correlations generates nodeless SC in the active planar $d_{xz,yz}$ bands, and an inter-band 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.