Superconductivity of systems with coexisting itinerant electrons and localpairs

Phase diagrams and electromagnetic properties of the system of coexisting i tinerant (c)-electrons and localized (d)-electrons which can form real spac e local pairs are analyzed. The model considered assumes arbitrary value of the on-site density interaction of d-electrons U-d, which allows investiga tion of the effects of reduced d-pair binding energy. The phase diagrams of the system have been evaluated within the approach which treats the on-sit e interaction term U-d exactly and the remaining interactions within the br oken symmetry HFA. Within the linear response theory the electromagnetic ke rnels axe calculated and basic superfluid characteristics of the system are determined as a function of electron concentration, interactions and relat ive position of the bands. Depending on parameters the model is found to ex hibit several kinds of superconducting behaviors ranging from the BCS-like to the local pair-like. The relevance of obtained results to the interpreta tion of experimental data for short-coherence length superconductors is poi nted out.