Out-of-Plane Momentum and Symmetry-Dependent Energy Gap of the PnictideBa0.6K0.4Fe2As2Superconductor Revealed by Angle-Resolved Photoemission Spectroscopy

Abstract

The three-dimensional band structure and superconducting gap of ${\mathrm{Ba}}_{0.6}{\mathrm{K}}_{0.4}{\mathrm{Fe}}_2{\mathrm{As}}_2$ are studied with angle-resolved photoemission spectroscopy. In contrast with previous results, we have identified three holelike Fermi surface sheets near the zone center with sizable out-of-plane or $k_z$ dispersion. The superconducting gap on certain Fermi surface sheets shows significant $k_z$ dependence. Moreover, the superconducting gap sizes are different at the same Fermi momentum for two bands with different spatial symmetries (one odd, one even). Our results further reveal the three-dimensional and orbital-dependent structure of the superconducting gap in iron pnictides, which facilitates the understanding of momentum-integrated measurements and provides a distinct test for theories.