From d-wave to s-wave pairing in the iron-pnictide superconductor (Ba,K)Fe<sub>2</sub>As<sub>2</sub>
From d-wave to s-wave pairing in the iron-pnictide superconductor (Ba,K)Fe<sub>2</sub>As<sub>2</sub>
The nature of the pairing state in iron-based superconductors is the subject of much debate. Here we argue that in one material, the stoichiometric iron pnictide KFe2As2, there is overwhelming evidence for a d-wave pairing state, characterized by symmetry-imposed vertical line nodes in the superconducting gap. This evidence is reviewed, …