CORE-LEVEL ELECTRONIC STATES OF THE YBA2CU3OYBRX SUPERCONDUCTOR STUDIED BY X-RAY PHOTOELECTRON-SPECTROSCOPY

Core-level electronic states of the YBa2Cu3OyBrx superconductor, tetragonal, and orthorhombic YBa2Cu3Oz, and BaBr2 have been studied with use of x-ray photoelectron spectroscopy. The intensity ratio of the satellite to Cu 2p3/2 line increases from 0.31 for the nonsuperconducting tetragonal phase to 0.46 for the brominated superconductor sample. The latter value is close to that for the superconducting orthorhombic phase (0.51), which strongly suggests that holes are doped by bromination into the tetragonal phase. Comparison of the binding energies of Ba 3d5/2 and Br 3d for the brominated sample with those of BaBr2 shows that bromine in the former sample is strongly interacting with barium. The mechanism for the recovery of the superconductivity is discussed in terms of hole doping.