Thermodynamic functions within the van Hove BCS model: symmetry mixing effects

Abstract

All the new layer perovskite superconductors seem to show a phenomenon of symmetry mixing with respect to the order parameters. An analysis of the different alternatives of mixing and how far they could be presented is carried out. For the particular case of s+ id symmetry of the gap, the temperature dependence of the specific heat ( C es) and the thermodynamic critical magnetic field ( H c) are calculated. A double peak transition is observed on C es( T) in the mixed regime while the single peak behavior is recovered for a purely symmetric state ( s or d). C es presents a quadratic law at low temperatures for a d-wave gap and the typical exponential attenuation for the s-wave. The temperature dependence of H c shows a clear phase transition of second order at temperatures where the d-wave component becomes negligible. A comparison with other results and experiments is done.