Abstract
Polarisation- dependent x-ray absorption spectroscopy at the Cu L3 and Ce M4,5 edges have been performed on the epitaxial films Nd1.85Ce0.15CuO4-δ vs. defect concentration induced by He+ ion irradiation. The Cu L3 edge exhibits increasing of integral intensity of both the white line in E||ab and the first peak in E||c by about 15% and 30%, respectively, after suppression of superconductivity. The partial filling of Ce 4f orbitals (~15%) takes place although the Ce ions remain formally tetravalent, Ce+4. Thus, XAS experiments give a clear evidence that the excess electrons leave Cu 3d10x2-y2 orbital and become simultaneously localised in the Ce-O(2) chains. The symmetry of the free states and the mechanism of superconductivity suppression in Nd1.85Ce0.15CuO4-δ under He+ ion irradiation are discussed.