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 hole-like and two electron-like bands in iron-based superconductors, we resolve one additional hole-like band around the zone center and one more fast-dispersing band near the X point in the vicinity of Fermi level. By tuning the polarization and the energy of incident photons,we are able to identify the specific orbital characters and the kz dependence of all bands. Combining with band calculations, we find As 4pz and 4px (4py) orbitals contribute significantly to the additional three-dimensional hole-like band and the narrow band, respectively. Also, there are considerable hybridization between the As 4p zand Fe 3d orbitals in the additional hole-like band, which suggests the strong coupling between the unique arsenic zigzag bond layers and the FeAs layers therein. Our findings provide a comprehensive picture of the orbital characters 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.
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