Electron spectroscopy of single-layer (n=1) Bi2Sr2-xLaxCuO6+delta crystalsat optimal doping

On single crystals of the single-layer (n = 1) high-T-c superconductor Bi2S r-LaxCuO6+delta at optimal doping (x = 0.4), the electron spectroscopies x- ray absorption (XAS) and high-resolution angle-resolved photoemission (ARPE S) were performed. The XAS gives the intensity of the so-called prepeak of the O 1s line what is due to the unoccupied part of the Zhang-Rice (ZR) sin glet band. For ARPES, the advantages of single-layer material are the absen ce of bilayer effects and the possibility to study the electronic propertie s of the normal state at a sample temperature where the thermal broadening is extremely small (<10 meV). The controlled variation of the polarization vector of the synchrotron radiation made it possible to resolve a distinct fine-structure of the occupied part of the ZR singlet band at the Fermi lev el. These observations have enormous consequences for line shape analyses a nd the determination of pseudogaps, and thus the mechanism of high-ir, supe rconductivity.