Observation of Strong-Coupling Pairing with Weakened Fermi-Surface Nesting at Optimal Hole Doping in Ca_0.33Na_0.67Fe₂As₂

We report an angle-resolved photoemission investigation of optimally doped Ca_0.33Na_0.67Fe₂As₂. The Fermi surface topology of this compound is similar to that of the well-studied Ba_0.6K_0.4Fe₂As₂ material, except for larger hole pockets resulting from a higher hole concentration per Fe atoms. We find that the quasi-nesting conditions are weakened in this compound compared to Ba_0.6K_0.4Fe₂As₂. Similar to Ba_0.6K_0.4Fe₂As₂, we observe nearly isotropic superconducting gaps with Fermi surface-dependent magnitudes for Ca_0.33Na_0.67Fe₂As₂. A small variation in the gap size along the momentum direction perpendicular to the surface is found for one of the Fermi surfaces. Our superconducting gap results on all Fermi surface sheets fit simultaneously very well to a global gap function derived from a strong coupling approach, which contains only 2 global parameters.