Robust accidental nodes and zeroes and critical quasiparticle scaling in iron-based multiband superconductors

TL;DR

This paper investigates multigap superconductivity in iron-based superconductors, revealing that accidental nodes in the gap function tend to persist at zero temperature and dominate quasiparticle behavior near quantum critical points.

Contribution

It demonstrates that accidental nodes in the superconducting gap often survive down to zero temperature and identifies a unique zero-point critical scaling in quasiparticle properties.

Findings

Accidental nodes in the gap function typically persist at T=0.

Zero-point critical scaling governs quasiparticle thermodynamics.

This scaling replaces traditional forms near quantum transitions.

Abstract

We study multigap superconductivity, with strong angular variations of one of the gaps, as appropriate for certain iron-based high-temperature superconductors. We solve the gap equations of this model and find that the nodes or zeroes in the gap function present at Tc - although purely accidental -- typically survive down to T=0. Based on this result, we investigate the line of quantum transitions at which gap zeroes first appear. The peculiar "zero-point" critical scaling emanating from this line dominates quasiparticle thermodynamics and transport properties over much of the phase diagram, and supplants more familiar forms of scaling associated with accidental nodes.