Ba core-level shift in x-ray photoemission spectroscopy on single-phase Y1-xPrxBa2Cu3O7 and YBa2Cu3O7-y compounds

We have measured x-ray photoemission spectra of single-phase Y1-xPrxBa2Cu3O7 (x=0.0, 0.2, 0.4, 0.6, 0.8) and of YBa2Cu3O7-y (y=0.0, 0.15, 0.40) compounds, in which superconductivity is suppressed by increasing x and y. Ba 3d and Ba 4d core-level spectra were observed to shift significantly towards higher binding energy as x and y increase, while Y 3d, Cu 3p, O 1s spectra were not. The shift of Ba core-level spectra is interpreted as resulting from a distinct initial-state Ba 5d-Od 2p covalency common to 1:2:3 structures, as opposed to final-state effects. This energy shift may constitute a sensitive fingerprint of the degree of hole localization at Ba sites, which is related to the quenching of superconductivity in these compounds.