HEAT CAPACITY OF YBa2Cu3O7−δ NEAR Tc

Abstract

The exceptionally short Ginzburg-Landau coherence length of the high temperature superconductor YBa 2 Cu 3 O 7−δ makes possible the observation of fluctuation effects near the transition from the normal to the superconducting state. At the time of this writing, observations of fluctuation contributions to the electrical conductivity,1 magnetic susceptibility2 and thermopower3 have been reported. Excess contributions to the heat capacity (C fl ) due to thermal fluctuations, though far more difficult to observe, have been noted by several researchers.4 The heat capacity measurements are of particular interest, as a comparison of C fl above and below T c may elucidate the number of components of the Ginzburg-Landau (GL) order parameter and hence the nature of the pairing. The behavior of the heat capacity in an applied magnetic field is distinctly different from that of an ordinary superconductor.5 We summarize here our results on heat capacity measurements in zero field and in an applied magnetic field.