THERMODYNAMICS OF ANISOTROPIC-GAP AND MULTIBAND CLEAN BCS SUPERCONDUCTORS

The free energy, non-gradient terms of the Ginzburg–Landau (GL) expansion, and the jump of the specific heat of a multiband anisotropic-gap BCS superconductor are derived in the framework of a separable-kernel approximation. Results for a two-band superconductor, d-wave superconductor, and some recent models for MgB2 are worked out as special cases of the general approach. The classical results for the GL coefficients are derived in a simple way, directly from the general expression for the free energy of a BCS superconductor.