O17nuclear-magnetic-resonance evidence for distinct carrier densities in the two types ofCuO2planes of (Bi,Pb)2Sr2Ca2Cu3Oy

Abstract

A study of ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ NMR spectra in the normal phase of ${}_{}{}^{17}{}_{}{}^{}\mathrm{enriched}$ powder samples of (Bi,Pb${)}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{Ca}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathit{y}}$ (2:2:2:3 phase) has allowed us to distinguish the NMR lines of the ${\mathrm{CuO}}_2$ planes having respectively pyramidal and square coordination for copper. The observed differences in the magnitude and temperature dependence of the ${}_{}{}^{17}{}_{}{}^{}\mathrm{O}$ 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.