Structural properties and magnetic behavior of the new iron-based superconductor CaKFe₄As₄

The iron-based superconductor CaKFe₄As₄ is one of the most famous representative of the new 1144 family of the iron pnictides. Because of the combination of alcali and alcaline-earth metals CaKFe₄As₄ is hole-doped itself and reaches a transition temperature of T_c = 35 K. We calculate ab initio the electronic structure and internal parameters by using density functional theory for several magnetic configurations. In contrast to other iron-based superconductors we find that the d_xy-orbital contributes not much to the Fermi-surface, whereas the d_x²-y²- and d_z²-orbitals are showing a strong contribution. This behavior is related to the shift of the FeAs-layer away from its high-symmetry position. Hereby we focus on the orbital-resolved electronic band-structure to estimate the strength of the electronic interactions.