Momentum dependence and nodes of the superconducting gap in iron-pnictides

TL;DR

This paper analyzes the superconducting gap structure in iron pnictides, showing how the interplay of intra-pocket repulsion and inter-band pair hopping determines whether the gap has nodes, with implications for understanding pairing mechanisms.

Contribution

It provides a theoretical framework linking the momentum dependence of the pairing interaction to the presence of nodes in the superconducting gap of iron pnictides.

Findings

Gaps with or without nodes can arise from the same pairing mechanism.

Stronger pair hopping leads to nodeless s+ gaps.

Weaker pair hopping results in nodal s+ gaps on electron Fermi surfaces.

Abstract

We discuss the structure of the superconducting gap in iron pnictides. In the itinerant electron picture, gaps with or without nodes have the extended s-wave (s+) symmetry and emerge within the same pairing mechanism, determined by the interplay between intra-pocket repulsion and inter-band pair hopping. If the pair hopping is stronger, the system develops an s+ gap without nodes. In the opposite case the superconductivity is governed by of the momentum-dependent part of the pair-hopping, and an s+ gap shows nodes on electron Fermi surfaces. We argue that the gap without/with nodes emerges in systems with a stronger/weaker tendency towards a spin-density-wave order.