Institution: | a Department of Synchrotron Radiation Research, Institute of Physics, Lund University, Box 118, S-221 00 Lund, Sweden b Materials Physics, Department of Physics, Royal Institute of Technology, S-100 44 Stockholm, Sweden c Russian Research Center ‘Kurchatov Institute', Kurchatov Square 1, 123182 Moscow, Russian Federation d Moscow State University, Department of Geology, 119 899 Moscow, Russian Federation e INFM-Dip. di Fisica, Politecnico di Milano, Piazza L. Da Vinci 32, I-20133 Milan, Italy |
Abstract: | Photoelectron spectroscopy results on single crystals of the superconductors Bi2Sr2CaCu2O8,Bi2Sr2CuO6, Ba0.6K0.4BiO3 and the semiconductor Ba0.9K0.1BiO3 are reported for the photon energy region around the O K absorption threshold. The development of the O-KVV Auger structure has been carefully monitored as a function of photon energy. A non-monotonic behavior displaying a feature at a constant binding energy of about 14 eV was found for Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 in a narrow photon energy region of 1 eV at the main edge of the O K absorption spectrum around 530 eV. The corresponding enhancement, connected with the autoionization of O 2p states, is absent in Ba1−xKxBiO 3 in contrast to Bi2Sr2CaCu2O8 and Bi2Sr2CuO6. The resonant enhancement is more pronounced for Bi2Sr2CuO6 as compared to Bi2Sr2CaCu2O8, which can be explained by a lower charge carrier concentration in the former case, leading to a more localized nature of intermediate O 2p states. The model parameters Cu d–d and O p–p Coulomb interactions and the charge transfer energy Δ are estimated from the experiments. |