Electronic Structure of Nd1.85Ce0.15CuO4-δIrradiated by He+Ions : An X-Ray Absorption Study on the Cu-L3and Ce-M4,5Edges

Abstract

Polarisation- dependent x-ray absorption spectroscopy at the Cu L 3 and Ce M 4,5 edges have been performed on the epitaxial films Nd 1.85 Ce 0.15 CuO 4-δ vs. defect concentration induced by He+ ion irradiation. The Cu L 3 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 3d 10 x 2― y 2 orbital and become simultaneously localised in the Ce-O(2) chains. The symmetry of the free states and the mechanism of superconductivity suppression in Nd 1.85 Ce 0.15 CuO 4-δ under He + ion irradiation are discussed.