Distribution of electrons and holes in cuprate superconductors as determined from 17O and 63Cu nuclear magnetic resonance.

The local distribution of electrons and holes in the CuO2 plane of the high-temperature superconducting cuprates is determined with nuclear magnetic resonance through the quadrupole splittings of 17O and 63Cu. Based on new data for single crystals of electron-doped Pr2-xCexCuO4 (x = 0, 0.05, 0.10, 0.15) as well as Nd2-xCexCuO4 (x = 0, 0.13) the changes in hole contents nd of Cu 3dx2-y2 and np of O 2pσ orbitals are determined and these account for the stoichiometrically doped charges, similar to hole-doped La2-xSrxCuO4. It emerges that while nd + 2np = 1 in all parent materials as expected, nd and np vary substantially between different groups of materials. Doping holes increases predominantly np, but also nd. To the contrary, doping electrons predominantly decreases nd and only slightly np. However, np for the electron-doped systems is higher than that in hole-doped La1.85Sr0.15CuO4. Cuprates with the highest maximum Tc's appear to have a comparatively low nd and high np. The rather high oxygen hole content of the Pr2CuO4 and Nd2CuO4 with the low nd seems to make them ideal candidates for hole doping to obtain a potentially high Tc. [ABSTRACT FROM AUTHOR]