H. Nylén

X-ray absorption study of oxygen in the high-Tc superconductor Bi2Sr2CaCu2O8 near the interfaces to Cu, Ag and Au

Abstract The influence on O 2p holes in single crystalline Bi 2 Sr 2 CaCu 2 O 8 upon the interface formation to Cu, Ag and Au has been studied by O K edge X-ray absorption measurements. It was found that Cu reduces the amount of doping induced O 2p holes significantly in the vicinity of the interface, whereas Ag and Au gave a much smaller reduction of these states. Photoemission spectra confirmed previous findings that Cu causes a strong chemical reaction at the BiO surface of Bi 2 Sr 2 CaCu 2 O 8 , in contrast to Ag and Au which induced only a minimal reaction. The results support the opinion that the BiO layers are essential for the doping of the CuO 2 layers in Bi 2 Sr 2 CaCu 2 O 8 .

O KVV Auger emission versus resonant photoemission at the O K edge of high-Tc superconductors

Abstract Photoelectron spectroscopy results on single crystals of the superconductors Bi 2 Sr 2 CaCu 2 O 8 ,Bi 2 Sr 2 CuO 6 , Ba 0.6 K 0.4 BiO 3 and the semiconductor Ba 0.9 K 0.1 BiO 3 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 Bi 2 Sr 2 CaCu 2 O 8 and Bi 2 Sr 2 CuO 6 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 2 p states, is absent in Ba 1− x K x BiO 3 in contrast to Bi 2 Sr 2 CaCu 2 O 8 and Bi 2 Sr 2 CuO 6 . The resonant enhancement is more pronounced for Bi 2 Sr 2 CuO 6 as compared to Bi 2 Sr 2 CaCu 2 O 8 , which can be explained by a lower charge carrier concentration in the former case, leading to a more localized nature of intermediate O 2 p states. The model parameters Cu d – d and O p – p Coulomb interactions and the charge transfer energy Δ are estimated from the experiments.

Surface electronic structure of Zn(0001) studied by angle resolved photoelectron spectroscopy

The surface electronic structure of Zn(0001) has been investigated by angle resolved photoelectron spectroscopy. A surface state around the M point, with a binding energy of 1.46 eV at M, was observed and thoroughly studied. The dispersion of this state is compared with the projection of the calculated three-dimensional bulk bands onto the surface Brillouin zone of the (0001) surface. The photoemission data concerning this state on Zn(0001) presented in here are compared with those measured on other nearly-free electron hexagonal close packed metals as well as with theoretical predictions.