  Here we report about the interface reconstruction in the recently discovered
superconducting artificial superlattices based on insulating CaCuO2 and SrTiO3
blocks. Hard x-ray photoelectron spectroscopy shows that the valence bands
alignment prevents any electronic reconstruction by direct charge transfer
between the two blocks. We demonstrate that the electrostatic built-in
potential is suppressed by oxygen redistribution in the alkaline earth
interface planes. By using highly oxidizing growth conditions, the oxygen
coordination in the reconstructed interfaces may be increased, resulting in the
hole doping of the cuprate block and thus in the appearance of
superconductivity.
