THE CRYSTALLINE ELECTRIC-FIELD AS A DIRECT PROBE FOR THE ELECTRON DOPING PROCESS IN ND2-XCEXCUO4

The neutron spectroscopic data available for the cuprates Nd2-χCeχCuO4 are analyzed towards establishing the crystalline electric field (CEF) interaction around the Nd3+ sites, which are situated close to the CuO2 planes and thus constitute a local probe of the charge distribution in these planes. Through a comparison of the CEF parameters in the insulating (χ=0) and superconducting (χ=0.15) state we find direct evidence for the addition of electrons to the CuO2 planes by doping Nd2CuO4 with Ce4+. While this compound is widely believed to be favourable for electron doping onto copper, our results indicate that the oxygen sites are also involved in the electron doping mechanism. © 1990.