SPECIFIC-HEAT AND THERMAL-EXPANSION OF THE BI AND TL HIGH-TEMPERATURE SUPERCONDUCTORS NEAR TC

We present measurements of the specific heat and of the thermal expansion of the most prominent phases of the Bi and Tl high temperature superconductors (Bi-2212, Bi-2223, Tl-2212, Tl-2223) in the neighbourhood of T(c). In all these systems we observe small but sharp anomalies which have very little similarity with the mean field jump found in the conventional superconductors. The analysis of these anomalies shows clear evidence for the presence of strong fluctuations of the order parameter. For temperatures more than almost-equal-to 5 K away from T(c), 2D Gaussian fluctuations are found, while within +/- 5 K of T(c) the fluctuation contribution is best fitted by critical fluctuations. The shape of the thermal expansion anomalies is similar to that of the specific heat. Combination of both measurements predicts dT(c)/dp almost-equal-to + 0.2 K/kbar for Bi- and Tl-2223 systems.