Abstract

The superconducting pairing of fermions is studied in the framework of the functional intergral approach. The bi-local composite scalar and vector fields are introduced to describe the singlet and triplet pairings. The static (time-independent) fields are the superconducting order parameters. From the variational principle for the effective action of the composite fields we derive the generalised Ginzburg–Landau equations. They are also the extensions of the BCS gap equations.