We investigated the type of the carriers doped in the CuO2-planes of non-superconducting Pr1+xBa2−xCu3O7 single crystals by nuclear magnetic resonance of Pr and chain-site Cu. The different spectra in the solid solution system show that the holes in Pr-rich crystals are localized in states similar to the ones in stoichiometric samples, that is in the 4f2−2pπ-hybridization band proposed by Fehrenbacher and Rice. In contrast, the spectra of crystals prepared under conditions favoring Ba-rich phases indicate the presence of holes in Zhang-Rice singlets in the CuO2-plane. Our results strongly support the model that superconductivity reported recently for Pr123-crystals is due to Ba-rich regions in the inhomogeneous samples.
@article{arxiv.cond-mat/9803336,
title = {Carrier doping in Pr_{1+x}Ba_{2-x}Cu_3O_7 studied by NMR},
author = {M. W. Pieper and F. Wiekhorst and T. Wolf},
journal= {arXiv preprint arXiv:cond-mat/9803336},
year = {2007}
}