Fermi surface geometry of heavily hole doped CaKFe4As4 revealed by angle-resolved photoemission spectroscopy

We have investigated Fermi surface geometry and band structure of CaKFe4As4 in which the FeAs layer is sandwiched by Ca and K layers. Using angle-resolved photoemission spectroscopy, the three hole pockets are observed around the zone center as commonly seen in various Fe-based superconductors. The outer hole pocket is significantly expanded around the Gamma point compared to that around the Z point. The area of the middle hole pocket is larger than that reported in the previous work [Mou et al., Phys. Rev. Lett. 117, 277001 (2016)] resulting in degraded Fermi surface nesting. The inner hole band is shifted downwards relative to the prediction of band structure calculations, and its top touches the Fermi level at the Gamma point. The discrepancy can be assigned to orbital dependent band renormalization of the Fe 3d bands. Due to the order of K and Ca layers, the hole bands at the Z point of the 122 phase are folded to the Gamma point in the 1144 phase increasing the interaction between the hole and electron bands irrespective of the poor Fermi surface nesting.