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 Ba1−xKxFe2As2, BaFe2−xCoxAs2, KxFe2−ySe2 and FeTe1−xSex (refs 1, 2, 3, 4), the signatures of nodal superconducting gaps have been reported in LaOFeP, LiFeP, KFe2As2, BaFe2(As1−xPx)2, BaFe2−xRuxAs2 and FeSe (refs 5, 6, 7, 8, 9, 10, 11, 12). We here report the angle-resolved photoemission spectroscopy measurements on the superconducting-gap structure of BaFe2(As0.7P0.3)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.
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Acknowledgements
The authors thank J. P. Hu and X. H. Chen for discussions, and thank D. H. Lu for the experimental assistance at SSRL. This work is supported in part by the National Science Foundation of China, Ministry of Education of China, Shanghai Municipal Science and Technology Committee and the National Basic Research Program of China (973 Program) under grant Nos 2012CB921400, 2011CB921802 and 2011CBA00112. SSRL is operated by the US Department of Energy, Office of Basic Energy Science, Divisions of Chemical Sciences and Material Sciences.
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Y.Z., Q.Q.G., Z.R.Y., F.C., M.X. and B.P.X. made ARPES measurements. Z.R.Y. and J.J. conducted sample characterization measurements. Z.R.Y. and Y.Z. grew the samples and analysed the ARPES data. D.L.F. and Y.Z. wrote the paper. D.L.F. is responsible for the infrastructure, project direction and planning.
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Zhang, Y., Ye, Z., Ge, Q. et al. Nodal superconducting-gap structure in ferropnictide superconductor BaFe2(As0.7P0.3)2. Nature Phys 8, 371–375 (2012). https://doi.org/10.1038/nphys2248
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DOI: https://doi.org/10.1038/nphys2248
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