The application of the fractional exclusion statistics to the BCS theory-A redefinition of the quasiparticle energies

The effective energy of a superconductor E-eff (T) at temperature T is defined as the difference between the total energy at temperature T and the total energy at 0 K. We call the energy of the condensate epsilon(c), the difference between E-eff and the sum of the quasiparticle energies E-qp. epsilon(c) ,E-qp, as well as the BCS quasiparticle energy epsilon are positive and depend on the gap energy Delta, which, in turn, depends on the populations of the quasiparticle states (equivalently, they depend on T). So, from the energetic point of view, the superconductor is a Fermi liquid of interacting quasiparticles.