Impurity substitution in bismuth and thallium cuprates: suppression of T-cand estimation of pseudogap

Suppression of T-c in bilayer bismuth and thallium cuprates by substitution of Co impurities at Cu sites were taken for examination. T-c suppression d ata on differently doped Bi2212 and Tl2212 were analysed within the unitary pair-breaking formalism due to Abrikosov and Gorkov, by fitting data point s to a phenomenological relation valid for weak coupling d-wave superconduc tors. Values of the pseudogap magnitude at each doping were thereby estimat ed within a "Fermi-level density of states suppression" picture. Pseudogap magnitude from our estimation was observed to have a correspondence with a related characteristic temperature T* obtained by thermoelectric power meas urements. Effects of pseudogap on the density of states were studied by cal culating the susceptibility, which shows a broad peak at high temperature. This peak feature in susceptibility is indicative of an unusual metallic st ale, which could be explored further by other systematic measurements. (C) 2000 Elsevier Science B.V. All rights reserved.