Significant Contribution Of As 4p Orbitals To The Low-Lying Electronic Structure Of The 112-Type Iron-Based Superconductor Ca0.9la0.1feas2

We report a systematic polarization-dependent angle-resolved photoemission spectroscopy study of the three-dimensional electronic structure of the recently discovered 112-type iron-based superconductor Ca1-xLaxFeAs2 (x = 0.1). Besides the commonly reported three holelike and two electronlike bands in iron-based superconductors, we resolve one additional holelike band around the zone center and one more fast-dispersing band near the X point in the vicinity of the Fermi level. By tuning the polarization and the energy of incident photons, we are able to identify the specific orbital character and the kz dependence of all bands. Combining these results with band calculations, we find that As 4p(z) and 4p(x) (4p(y)) orbitals contribute significantly to the additional three-dimensional holelike band and the narrow band, respectively. Also, there is considerable hybridization between the As 4pz and Fe 3d orbitals in the additional holelike band, which suggests strong coupling between the unique arsenic zigzag bond layers and the FeAs layers therein. Our findings provide a comprehensive picture of the orbital character of the low-lying band structure of 112-type iron-based superconductors, which can be a starting point for the further understanding of their unconventional superconductivity.