O-17 NMR EVIDENCE FOR DISTINCT CARRIER DENSITIES IN THE 2 TYPES OF CUO2 PLANES OF (BI,PB)2SR2CA2CU3OY

A study of O-17 NMR spectra in the normal phase of O-17-enriched powder samples of (Bi,Pb)2Sr2Ca2Cu3O(y) (2:2:2:3 phase) has allowed us to distinguish the NMR lines of the CuO2 planes having, respectively, pyramidal and square coordination for copper. The observed differences in the magnitude and temperature dependence of the O-17 Knight shift of the two types of planes are consistent with the occurrence of stronger electron correlations, or smaller carrier density, in the plane-square coordinated planes, in accordance with recent theoretical predictions.