Experimental survey of critical fluctuations in the specific heat of high-temperature superconductors

Thermal fluctuations are observed in the specific heat of high-temperature superconductors (HTS) near T-c. This is seen both in the shape of the zero- field anomaly, characterized by critical exponents and amplitude ratios, an d in the broadening of the transition versus the magnetic held, which obeys scaling laws. 3D-XY fluctuations are found for YBa2Cu3Ox (Y-123) near opti mal doping, whereas systematic deviations occur away from this point. The l arge deviations found for the most anisotropic PITS may be attributed to bo th reduced dimensionality and a crossover between BCS and Bose condensation s. Pow-temperature data are discussed in this contest. The melting curve of vortex matter, now detected in the specific heat of Dy-123, Eu-123 and Y-1 23 up to very high fields! is described by a critical exponent. (C) 2000 El sevier Science B.V. All rights reserved.