Relation between nodes and2Δ/Tcon the hole Fermi surface in iron-based superconductors

Abstract

We analyze the interplay between the absence or presence of nodes in the superconducting gap along electron Fermi surfaces (FSs) in Fe pnictides and $2\ensuremath{\Delta}/{T}_{c}$ along hole FSs ($2{\ensuremath{\Delta}}_{h}/{T}_{c}$), measured by angle-resolved photoemission spectroscopy (ARPES). We solve the set of coupled gap equations for 4- and 5-pocket models of Fe pnictides and relate the presence of the nodes to $2{\ensuremath{\Delta}}_{h}/{T}_{c}$ being below a certain threshold. Using ARPES data for $2{\ensuremath{\Delta}}_{h}/{T}_{c}$, we find that the optimally doped ${\text{Ba}}_{1\ensuremath{-}x}{\text{K}}_{x}{\text{Fe}}_{2}{\text{As}}_{2}$ and $\text{Ba}({\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x}){}_{2}{\text{As}}_{2}$ are likely nodeless, but isovalent ${\text{BaFe}}_{2}({\text{As}}_{1\ensuremath{-}x}{\text{P}}_{x}){}_{2}$ likely has nodes.