Superconducting gap symmetry of Ba0.6K0.4Fe2As2 studied by angle-resolved photoemission spectroscopy

We have performed high-resolution angle-resolved photoemission spectroscopy on the optimally doped Ba0.6K0.4Fe2As2 compound and determined the accurate momentum dependence of the superconducting (SC) gap in four Fermi-surface sheets including a newly discovered outer electron pocket at the M-point. The SC gap on this pocket is nearly isotropic and its magnitude is comparable (Delta similar to 11meV) to that of the inner electron and hole pockets (similar to 12 meV), although it is substantially larger than that of the outer hole pocket (similar to 6meV). The Fermi-surface dependence of the SC gap value is basically consistent with the Delta(k)=Delta(0) cos k(x) cos k(y) formula expected for the extended s-wave symmetry. The observed finite deviation from the simple formula suggests the importance of multi-orbital effects. Copyright (C) EPLA, 2009