The properties of systems consisting of a mixture of local electron pairs and itinerant fermions coupled via charge exchange mechanism, which mutually induces superconductivity in both subsystems, are analyzed. The case of anisotropic pairing of various symmetries is discussed in detail for a two-dimensional (2D) square lattice within the BCS-mean field approximation and the Kosterlitz-Thouless theory. The effects of electronic band dispersion as well as a quasi-2D case with interplanar hopping of electrons are also briefly analyzed. We determined the phase diagrams and superconducting characteristics as a function of the position of the local pair (LP) level and the total electron concentration. The possible types of crossovers from BCS like behavior to that of LP’s are examined. In addition, the Uemura plots are obtained for extended s and $d_{x^2-y^2}$ pairing symmetries. Some of our findings are discussed in connection with a two-component scenario of preformed pairs and unpaired electrons for the cuprate high-temperature superconductors.

• Received 15 May 2002

DOI:https://doi.org/10.1103/PhysRevB.66.104516