Specific heat and magnetoresistance of Y-, Tl- and Bi-type high temperature superconductors

Specific heat of polycrystalline DyBa2Cu3O7 and Tl0.58Pb0.42Sr1.6Ba0.4Ca2Cu3O9 samples as well as the single crystal of Bi2Sr2CaCu2O8 have been measured within the temperature interval from 50 to 250 K. Dy- and Tl-specimens the pronounced jump in specific heat and apparent contribution from Gaussian fluctuations of superconducting order parameter close to Tc have been observed. In contrary, in Bi- specimen only a rounded maximum within a broad interval around Tc has been detected. Magnetoresistance measurements as a function of temperature just below Tc have been carried out for Dy- and Tl-samples and the slopes of upper critical fields have been determined. The data have been analysed within the frame of Ginzburg-Landau-Abrikosov-Gorkov theory with additional Gaussian-like fluctuation theorem. The electronic specific heat coefficients γ, and the coherence length ξ have been obtained. (author)