DISCONTINUOUS PHASE-TRANSITIONS IN S-PAIRED FERMI SYSTEMS

The most general S-paired systems of fermions for which a gap equation can be separated according to the specific redefined variables, are c onsidered. Moreover, a solution of this gap equation (gap energy) is o btained in a parametric form. It allows us to investigate thermodynami c properties of such systems i.e. the thermodynamic potential, entropy , heat capacity and critical magnetic induction. We show also that the heat capacity difference between the superconducting and the normal p hase is entirely determined by the order parameter. The obtained resul ts reveal possibilities of discontinuous phase transition to the norma l state and moreover, the theorem on existence of such transitions is formulated and proved. The condition for the BCS-type energy gap is gi ven, which additionally classifies properties of the heat capacity of S-paired phase by virtue of the shape of the energy gap. In order to i llustrate the developed formalism, the numerical results for the so-ca lled statistical spin liquids and application of the established metho ds to the experimental data conversion, are presented and discussed.