Thermodynamics of extended s-wave superconductor

Abstract

We have calculated the specific heat for a model of an extended s-wave superconductor. When the coupling in the constant- channel (PI, pure isotropic) dominates over the anisotropic-channel (PA, pure anisotropic), the specific heat jump starts at the canonical value 1.43, decreases monotonically with increasing PI-PA mixing λ 1 and saturates at 1.43[4/[7+4α 3+α 4]]≡ R for λ 1→∞. Here α 3 and α 4 are, respectively, the average of cube and fourth power of the PA part which could be a Fermi surface harmonic. When the PA part is larger than the PI part coupling, the specific heat jump starts at the smaller value of 1.43/α 4, exhibits a minimum and then saturates to the same value R as λ 1→∞. In both cases, PI-PA mixing decreases the jump over the pure state value.