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 δC/C<0.02%. This simple and fast DTA method is suitable not only to detect the specific-heat discontinuity at Tc of high-temperature superconductors, but also to study the thermodynamics at the irreversibility boundary Hirr(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 Hirr(T), namely L<0.05kBT per vortex per layer for an external field μ0H=7 T parallel to the c axis of the investigated specimen