Nodal superconducting-gap structure in ferropnictide superconductor BaFe 2 (As 0.7 P 0.3) 2

Abstract

The superconducting-gap distribution is a pivotal characteristic for a superconductor. Whereas the cuprates and conventional phonon-mediated superconductors are characterized by distinct d-wave and s-wave pairing symmetries with nodal and nodeless gap distributions respectively, the superconducting-gap distributions in iron-based superconductors are rather diversified. Whereas nodeless gap distributions have been directly observed in Ba 1-x K x Fe 2 As 2, BaFe 2-x Co x As 2, K x Fe 2-y Se 2 and FeTe 1-x Se x (refs 1-4, the signatures of nodal superconducting gaps have been reported in LaOFeP, LiFeP, KFe 2 As 2, BaFe 2 (As 1-x P x) 2, BaFe 2-x Ru x As 2 and FeSe (refs 5-12). We here report the angle-resolved photoemission spectroscopy measurements on the superconducting-gap structure of BaFe 2 (As 0.7 P 0.3) 2, and in particular the direct observation of a circular line node on the largest hole Fermi surface around the Z point at the Brillouin zone boundary. Our findings rule out a d-wave-pairing origin for the nodal gap, and establish the existence of nodes in iron pnictides under the s-wave pairing symmetry. © 2012 Macmillan Publishers Limited. All rights reserved.