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

TL;DR

This paper investigates the effects of symmetry mixing in the order parameter of layer perovskite superconductors, analyzing thermodynamic functions like specific heat and critical magnetic field, revealing phase transitions and characteristic behaviors.

Contribution

It provides a detailed analysis of symmetry mixing effects on thermodynamic properties in the van Hove BCS model, especially for s+id symmetry, including temperature-dependent behaviors and phase transition insights.

Findings

Double peak transition in specific heat for mixed symmetry

Quadratic low-temperature behavior for d-wave gap

Second order phase transition when d-wave component vanishes

Abstract

All the new layer perovskite superconductors seem to show a phenomenon of symmetry mixing with repect to the order parameter. An analysis of the different alternative of mixing and how far could them 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 tempeartures for a d-wave gap and for the s-wave one the typical exponential attenuation. 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.