The influence of doping on the electronic structure of R 1− xCa xBa 2Cu 3O 6+ d (R=Y, Eu) and (La 0.7Ca 0.3) 1− xMn 1+ xO 3

Abstract

The valence band and core level states of R 1− x Ca x Ba 2Cu 3O 6+ d (R = Y, Eu) and (La 0.7Ca 0.3) 1− x Mn 1+ x O 3 systems were studied by means of angle integrated photoemission. The measurements have been performed on deoxygenated R 1− x Ca x Ba 2Cu 3O 6.1 samples which were insulators or superconductors depending on the calcium content as well as on oxygenated high T c RBa 2Cu 3O 6.9 superconductors. The goal was to study the effect of doping on the valence band and core level states and observe the change in the electronic structure. The studies of the valence band show an increase in the number of states located at 2.5 eV below the Fermi level. The parameters of the electronic structure are estimated (by cluster model calculations) to be: Δ∼1 to 2 eV, T∼2.5–3.5 eV and U dd∼6.5 eV. The valence band spectra of (La 0.7Ca 0.3) 1− x Mn 1+ x O 3 ( x=0, 0.1) are very similar showing two peaks at about 3.5 and 5.7 eV for x=0 and at 6.0 and 7.7 eV for x=0.1 below the upper edge of the valence band. These indicate partly hybridized Mn 3d–O 2p states. From the Mn 2p spectrum and its comparison with the relevant Auger spectrum values of the charge transfer energy Δ, the hybridization energy between Mn 3d and O 2p states T and the on site Coulomb correlation energies U dd in Mn 3d and U pp in O 2p states were estimated to be about 5, 4, 4 and 6.5 eV, respectively. These results indicate the mixed character of the ground state.