SUPERCONDUCTIVITY OF SYSTEMS WITH COEXISTING ITINERANT ELECTRONS AND LOCAL PAIRS

Abstract

Phase diagrams and electromagnetic properties of the system of coexisting itinerant (c)-electrons and localized (d)-electrons which can form real space local pairs are analyzed. The model considered assumes arbitrary value of the on-site density interaction of d-electrons U d , which allows investigation 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-site interaction term U d exactly and the remaining interactions within the broke symmetry HFA. Within the linear response theory the electromagnetic kernels are calculated and basic superfluid characteristics of the system are determined as a function of electron concentration, interactions and relative position of the bands. Depending on parameters the model is found to exhibit several kinds of superconducting behaviors ranging from the BCS-like to the local pair-like. The relevance of obtained results to the interpretation of experimental data for short-coherence length superconductors is pointed out.