A POLARIZED X-RAY-ABSORPTION SPECTROSCOPY STUDY OF O-K AND CU-L-3 EDGES IN A TL(2212) THIN-FILM

A reliable estimate of the density of state shaving in-plane and out-o f-plane symmetry in the O K-edge and the Cu L-3-edge polarized spectra is important for checking the validity of several theoretical models which predict an active role for these states in the mechanism of supe rconductivity. In the present contribution, we report on our fluoresce nce yield O K-edge and Cu L-3-edge polarized spectra obtained for a we ll characterized and oriented overdoped Tl(2212) thin film as well as our simultaneous fluorescence-and total-yield Cu L-3 measurements on a n optimally doped T1(2212) thin film. Our results show that a signific ant number of out-of-plane O 2p(z) and Cu 3d(z2-r2) holes also exist i n thallium cuprates, more so in the overdoped case, and that use of th e bulk-sensitive fluorescence technique is better for obtaining a reli able estimate of the density and symmetry of these roles. The spectra are compared with those reported earlier for other cuprate systems and are interpreted in terms of the available band-structure calculations . No direct correlation between superconductivity and the presence or absence of out-of-plane covalent and doping hole densities appears pla usible, so theories based on the existence of a large density of such holes appear to be inconsistent with the experiment.