Relation between 2Delta/Tc and nodes in Fe-based superconductors

TL;DR

This paper investigates how the presence of nodes in the superconducting gap of Fe-based superconductors correlates with the ratio 2Delta/Tc, using theoretical models and ARPES data to identify nodeless and nodal behaviors.

Contribution

It establishes a relationship between gap nodes and 2Delta/Tc thresholds through coupled gap equations and ARPES measurements, providing insights into the nodal structure of Fe-pnictides.

Findings

Optimally doped BaKFe2As2 and Ba(FeCo)2As2 are likely nodeless.

BaFe2(AsP)2 likely has nodes in the superconducting gap.

Presence of nodes correlates with 2Delta/Tc being below a certain threshold.

Abstract

We analyze the interplay between the absence or presence of the nodes in the superconducting gap along electron Fermi surfaces (FSs) in Fe-pnictides, and 2Delta/T_c along hole FSs, measured by ARPES. We solve the set of coupled gap equations for 4-band and 5-band models of Fe-pnictides and relate the presence of the nodes to 2\Delta/T_c being below a certain threshold. Using ARPES data for 2\Delta/T_c, we find that optimally doped (BaK)Fe_2As_2 and Ba(FeCo)_2As_2 and likely nodeless, but iso-valent BaFe_2(AsP)_2 likely has nodes.