Distinct evolution of charge occupations on Fe 3d orbitals in hole-doped iron arsenic superconductors

First-principles calculations are performed to study the hole doping effect in a series of iron arsenic superconductors, such as the undoped CaFe2As2, CaFeAsF, and the hole-doped CaKFe4As4, KCa2Fe4As4F2, and KFe2As2. Charge occupations in the Fe 3d orbitals are found to show opposite variations when the filling is changed. Compared with the undoped CaFe2As2 and CaFeAsF, charges of the and orbitals decrease while those of the and d xy orbitals increase in the hole-doped materials CaKFe4As4, KCa2Fe4As4F2 and KFe2As2. By further analyzing the Pauli susceptibilities of CaFe2As2 and CaFeAsF, instability is found at the wave vector of , which is responsible for the stripe type antiferromagnetic order. In contrast, the Pauli susceptibilities of CaKFe4As4 and KCa2Fe4As4F2 at are strongly suppressed while the instabilities remain around , which may be the origin of superconductivity. Combining with the calculated orbital-resolved Pauli susceptibility, we conclude that hole doping mainly results in a decrease of charge occupations in the and orbitals, and these three orbitals play dominant roles in controlling the magnetic and superconducting properties in these iron-based superconductors.