Carrier doping in Pr_{1+x}Ba_{2-x}Cu_3O_7 studied by NMR

摘要

We investigated the type of the carriers doped in the CuO$_2$-planes ofnon-superconducting Pr$_{1+x}$Ba$_{2-x}$Cu$_3$O$_7$ single crystals by nuclearmagnetic resonance of Pr and chain-site Cu. The different spectra in the solidsolution system show that the holes in Pr-rich crystals are localized in statessimilar to the ones in stoichiometric samples, that is in the$4f^2-2p\pi$-hybridization band proposed by Fehrenbacher and Rice. In contrast,the spectra of crystals prepared under conditions favoring Ba-rich phasesindicate the presence of holes in Zhang-Rice singlets in the CuO$_2$-plane. Ourresults strongly support the model that superconductivity reported recently forPr123-crystals is due to Ba-rich regions in the inhomogeneous samples.