Xu, Y-M.Huang, Y-B.Cui, X-Y.Razzoli, E.Radovic, M.Shi, M.Chen, G-F.Zheng, P.Wang, N-L.Zhang, C-L.Dai, P-C.Hu, J-P.Wang, Z.Ding, H.2011-12-162011-12-162011-12-16201110.1038/NPHYS1879https://infoscience.epfl.ch/handle/20.500.14299/74383WOS:000287844300015The iron-pnictide superconductors have a layered structure formed by stacks of FeAs planes from which the superconductivity originates. Given the multiband and quasi three-dimensional(1) (3D) electronic structure of these high-temperature superconductors, knowledge of the quasi-3D superconducting (SC) gap is essential for understanding the superconducting mechanism. By using the k(z) capability of angle-resolved photoemission, we completely determined the SC gap on all five Fermi surfaces (FSs) in three dimensions on Ba0.6K0.4Fe2As2 samples. We found a marked kz dispersion of the SC gap, which can derive only from interlayer pairing. Remarkably, the SC energy gaps can be described by a single 3D gap function with two energy scales characterizing the strengths of intralayer Delta(1) and interlayer Delta(2) pairing. The anisotropy ratio Delta(1)/Delta(2), determined from the gap function, is close to the c-axis anisotropy ratio of the magnetic exchange coupling J(c)/J(ab) in the parent compound(2). The ubiquitous gap function for all the 3D FSs reveals that pairing is short-ranged and strongly constrains the possible pairing force in the pnictides. A suitable candidate could arise from short-range antiferromagnetic fluctuations.text::journal::journal article::research article