Photoelectron Spectroscopic Study of Tl-2201, Tl-2212, Tl-2223, and Tl-2234 High-T_c Superconductors

Abstract

A comparative photoelectron spectroscopic study of high quality polycrystalline T1_1.8Ba₂Cu_1.2O_x (Tl2201), Tl₂Ba₂CaCu₂O_x (Tl2212), Tl_1.7Ba₂Ca_2.3Cu₃O_y (Tl2223), and T_1.7Ba₂Ca_3.3Cu₄O_z (T12234) superconductors was performed. The binding energies of T14f core-levels reveal that the valences of Tl in these compounds are in between 1+ and 3+ and nearly identical. This seems to be an additional mechanism unique to Tl- HTSC’s to introduce hole-carriers into the systems. Comparison of the valence band region spectra made it possible to identify the Ca3p origin band uniquely. From UPS valence band spectra, in addition to the peaks at about 3eV and 5eV below the Fermi level which are common to all copper oxide HTSC’s, it is likely that a peak at about 9.5 eV is intrinsic for Tl systems. Finite density of states without sharp egde were observed at the Fermi level and the results are discussed in comparison with those of Bi-HTSC’s.