CALORIMETRIC STUDY OF YBA2CU3O6.92 IN VERY HIGH MAGNETIC-FIELD - 27 TESLA

The specific heat of a large YBa2Cu3O6.92 single crystal (m approximate to 150 mg) was measured between 0 and 27 Tesla. In contrast with previous results obtained at lower fields, the specific heat above T-c is field-dependent up to 100 K. The high magnetic fields combined with a narrow transition width (Delta T-c(10-9%)=0.15 K in ac susceptibility) allow an accurate analysis of the different contributions in the vicinity of T-c(H=0). 2D-3D gaussian and 3D-xy critical fluctuations models are compared. A positive curvature of the H-c2(T) line is observed up to 10 Tesla. The compatibility of the calorimetric and magnetic measurements [1] through Maxwell's relation is also verified.