J. Phys. IV France 7 (1997) C2-1123-C2-1124
Electronic Structure of Nd1.85Ce0.15CuO4-δ Irradiated by He+ Ions : An X-Ray Absorption Study on the Cu-L3 and Ce-M4,5 EdgesA.Yu. Ignatov1, S. Iacobucci2, 3, A.P. Menushenkov1, P. Lagarde2 and A.A. Ivanov1
1 Moscow Engineering Physics Institute, Kashirskoe sh. 31, 115409 Moscow, Russia
2 Laboratoire pour l'Utilisation du Rayonnement Electromagnétique, Centre Universitaire Paris-Sud, Bât. 209D, 91405 Orsay, France
3 IMAI CNR, Area della Ricerca di Roma, Salaria, 00016 Monterotondo, Italy.
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.
© EDP Sciences 1997