Superconductivity in the Infinite Layer Compound CaCuO2

Superconductivity in the electric field-effect doped infinite layer compound CaCuO2 is considered. It is argued that in the superconducting CuO2 layer, next to the insulating Al2O3 overlayer, the coordination of the Cu2+ ions by oxygens is pyramidal rather than square planar. This view stems from existing NEXAFS and the analysis of HRETM results, as well as chemical considerations, and is discussed mainly for the hole doped but also the electron doped region of the phase diagramm.