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

Abstract

We investigated the type of the carriers doped in the CuO${}_2$-planes of non-superconducting Pr${}_{1+x}$Ba${}_{2-x}$Cu${}_3$O${}_7$ 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 $4f^2-2p\pi$-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 CuO${}_2$-plane. Our results strongly support the model that superconductivity reported recently for Pr123-crystals is due to Ba-rich regions in the inhomogeneous samples.

4 pages, 3 figures