HIGH-ACCURACY DIFFERENTIAL THERMAL-ANALYSIS - A TOOL FOR CALORIMETRIC INVESTIGATIONS ON SMALL HIGH-TEMPERATURE-SUPERCONDUCTOR SPECIMENS

We describe a technique for measuring small heat capacities below room temperature, which represents a simple but significant improvement of the conventional differential thermal-analysis (DTA) method by means of high-precision electronic components. It is thereby possible to measure the heat capacity C(T) of milligram samples with a relative accuracy delta C/C < 0.02%. This simple and fast DTA method is suitable not only to detect the specific-heat discontinuity at T-c of high-temperature superconductors, but also to study the thermodynamics at the irreversibility boundary H-irr(T) in the magnetic phase diagram of cuprate superconductors. From respective measurements on a YBa2Cu3O7 single crystal, we deduce an upper limit for a latent heat L associated with a hypothetical first-order transition at H-irr(T), namely L < 0.05k(B) T per vortex per layer for an external field mu(0)H=7 T parallel to the c axis of the investigated specimen.