The specific heat anomalies at Tc of the BiSrCaCuO and TlBaCaCuO high temperature superconductors

In the specific heat of the BiSrCaCuO and TlBaCaCuO families of high temperature superconductors the usual jump of a second order mean field transition is absent. Sharp breaks of the slope of C(T) appear instead at the thermodynamic transition temperature TGL, and in high quality samples a small dip appears in C(T) at TKT, 1-1.5 K below TGL, where the dc Meissner effect sets in. Corresponding anomalies are seen in the thermal expansion, in the resistivity and in the Hall effect. It is argued that strong intrinsic fluctuations broaden the mean field anomalies, e.g by ±10K in the case of Bi2Sr2Ca2Cu3Ox.