Electronic band structure of SrCu₄As₂ and KCu ₄As₂: Metals with diversely doped CuAs layers

We present a density functional study of SrCu₄As₂ and KCu₄As₂. The two isostructural compounds constitute a system that allows a broad range of doping of CuAs layers through nominally K⁺ for Sr2⁺ substitution. SrCu₄As₂ (space group R3̄m) is a metal having highly dispersive bands at E _F, two holelike Fermi sheets in the form of corrugated cylinders along Γ-Z and electron pockets around F points in the rhombohedral Brillouin zone. Cu 3d states are located at 2.5 eV below E_F, giving little contribution to the bands near E_F. The F-point electron pockets disappear in KCu₄As₂ and the compound exhibits a large multisheet two-dimensional Fermi surface with a somewhat enhanced d character through Cu 3d-As 4p bonding. Despite shifting E_F toward the Cu 3d bands in KCu₄As₂, the compound remains with completely populated d shells and it is unlikely to exhibit superconductivity of a type similar to that in the ternary iron arsenides.