Electronic structure of YBa2Cu3O7-δ as a function of δ : determination of the valency of copper atoms by X-ray absorption and photoemission experiments

Abstract

The electronic structure of YBa2Cu3O7- δ compounds has been studied in the range 0 < 8 < 1, by performing X-ray Absorption (XAS) on the Cu K edge and X-ray Photoemission experiments (XPS) on the Cu2p and O1s core levels. The absorption experiments have been performed by following continuously the Copper K edge during isothermal cycles of oxy-deoxygenation. Such experiments bring the absolute modifications of the electronic structure, thus minimizing the use of reference compounds in the discussion. An highly correlated mixed-valent ground state in these high Tc materials is suggested. A comparison with the XPS results is made and it confirms this assumption.