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 Ud, 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 Ud 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.
International Journal of Modern Physics B
- Pub Date:
- Theories and models of superconducting state;
- Nonconventional mechanisms;
- Narrow-band systems;
- intermediate-valence solids