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

¹ School of Physics and Optoelectronic Engineering, Ludong University - Yantai 264025, China
² Shanghai Key Laboratory of Special Artificial Microstructure Materials and Technology, School of Physics Science and Engineering, Tongji University - Shanghai 200092, China

^(a) mcding@ldu.edu.cn (corresponding author)
^(b) yzzhang@tongji.edu.cn (corresponding author)

Received: 12 September 2020
Accepted: 28 November 2020

Abstract

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.