Comparative photoemission studies of Tl2Ba2Can-1CunO2n+4 (n=1, 2, and 3)

Detailed studies on the bi-Tl layer family of cuprate superconductors for the first three members have been carried out by valence-level and core-level photoemission. Ca 2p and Ba 3d core levels show a variation in broadening with an increasing number of CuO2 planes. The Tl 4f core level shows a mixed valent character [Tl(I) and Tl(III)] in all the three samples. The Cu 2p core-level spectrum also shows a change in the satellite to main line intensity and the energy difference between them. Simplified configuration interaction calculations are carried out to explain the observed changes. A rigid shift of the valence band is observed with the increase in the number of CuO2 planes. Near-Fermi-level features are identified as due to a Kondo-type resonance and resulting heavy-electron band states.