SPECIFIC-HEAT OF HIGH-TEMPERATURE SUPERCONDUCTORS IN HIGH MAGNETIC-FIELDS

We review investigations of the mixed-state specific heat (C) of extre me type-II superconductors in magnetic fields B less than or equal to 16 T, from 1 K to T-c. In YBa2Cu3Ox (Y123) at low temperature T, a sca ling law Delta C proportional to(TB1/2)f(T/B-1/2), which is a signatur e of d-wave symmetry, is observed for the background-free anisotropic component Delta C=C(B//c)-C(B//ab). At intermediate T, a C(B)-C(0)prop ortional to T(n)BlnB behaviour, which may be explained by the London m odel, smoothly sets in. Near T-c, superconducting fluctuations are inv estigated using the background-free derivative partial derivative(C/T) partial derivative B. 3D-XY scaling properties are verified up to the overdoped regime. Fluctuations obey different laws in Bi2Sr2CaCu2Ox (B i2212), which is strongly affected by its 2D character. Finally, the m elting line of the vortex solid, which is now believed to be the only true phase transition above H-cl in the presence of fluctuations, is o bserved in Y123 either as a 1st- or 2nd-order transition, depending on pinning.