Superconductivity in Hubbard models coupled to non-fermionic degrees of freedom

We explore the consequences of coupling between repulsive Hubbard models and Bosonic or spin degrees of freedom. In the regime where the characteristic energy of the non-fermionic part is large compared to the characteristic energy of the Fermions, the effective Hamiltonian corresponds to a generalized attractive Hubbard model. Superconducting properties are then calculated within the BCS scheme including the finite size dependence of correlation functions functions characterizing s-wave pairing. © 1990 Springer-Verlag.