X-ray photoelectron spectra of high Tc bismuth compounds : General trends for layer structures

Abstract

Analysis by XPS and XAES has been carried out for Bi2Sr2CaCu2O8 and Bi2Sr2CuO6 HTSC compounds. Some preliminary results are also reported for a Tl specimen with predominant Tl2Ba2CaCu2O8 stoichiometry, as well as La0.6Sr0.4CoO3 which is a metallic oxide, but is not superconducting above 4.2 K. Anomalous low binding energy contributions are found for the main alkaline earth envelopes (Ba 3d, Ca 2p, and Sr 3d) for all of these compounds. Likewise, two distinct contributions to the O 1s envelope are observed. The Bi and Tl 4f envelopes and binding energies are consistent with these species being subject to metallic screening. Possible implications of these observations for the electronic structure of the layered HTSC oxides are discussed in the context of a screening as well as a shake-down model.