Electronic properties, low-energy Hamiltonian, and superconducting instabilities in CaKFe₄As₄.

We analyze the electronic properties of the recently discovered stoichiometric superconductor CaKFe₄As₄ by combining an ab initio approach and a projection of the band structure to a low-energy tight-binding Hamiltonian, based on the maximally localized Wannier orbitals of the 3d Fe states. We identify the key symmetries as well as differences and similarities in the electronic structure between CaKFe₄As₄ and the parent systems CaFe₄As₄ and KFe₂As₂. In particular, we find CaKFe₄As₄ to have a significantly more quasi-two-dimensional electronic structure than the latter systems. Finally, we study the superconducting instabilities in CaKFe₄As₄ by employing the leading angular harmonics approximation and find two potential A_1g-symmetry representations of the superconducting gap to be the dominant instabilities in this system.