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SUPERCONDUCTIVITY IN SYSTEMS WITH LOCAL ATTRACTIVE INTERACTIONS

We discuss approaches based on the concepts of local electron pairing and the superconducting properties which they imply. The nature of the intermediate coupling regime is addressed and a recent progress in the BCS–Bose superconductivity crossover problem is outlined. We also survey the properties of systems with local attractive interactions consisting of a mixture of local electron pairs and itinerant fermions coupled via a charge exchange mechanism which mutually induces superconductivity in both subsystems. Finally, we briefly discuss the question of a pseudogap and a possible scenario of crossovers in high temperature superconductors.