Specific heat of the local-pair superconductor

Abstract

The temperature dependence of the specific heat C( T) of the local-pair (LP) superconductor is calculated in the mean-field-random-phase-approximation, using the mapping of the LP model at constant carrier density onto the anisotropic Heisenberg pseudo-spin system at constant magnetization. Both the 3D and quasi 2D (highly anisotropic) LP superconductors are investigated, both for a small carrier concentration n. Below T c, C( T) obeys power laws with different exponents in the 3D and quasi 2D cases, and rises steeply as T approaches T c. Above T c the model predicts a linear T-dependence for C( T) for the quasi 2D case in a substantial temperature range before C( T) reaches its classical value ≈ n. Such a contribution to C( T) above T c has been reported in some experiments. The model may also account for the small values for entropy at T c found in the experiments in the superconducting oxides. For temperatures much bigger than the LP-band width, we find C( T)∼ T −2 in both cases, in agreement with ref. [5] (R. Micnas et al., Rev. Mod. Phys. 62 (1990) 113).