MAGNETIC ASPECTS OF SUPERCONDUCTING PAIRING

We discuss some of the recently proposed models dealing with the super conducting state in the presence of strong antiferromagnetic fluctuati ons, induced by the on-site Coulomb repulsion between electrons (the H ubbard correlation). In the weak coupling limit we treat the influence of correlation effects on the phonon-mediated superconductivity withi n the BCS-Eliashberg framework. As a non-standard model in this limit we describe next the so-called spin bag model. To discuss strong corre lation limit, we describe first the projected Hamiltonian (the t-J Ham iltonian) and the corresponding antiferromagnetic state. The resonatin g valence bond model is introduced both as a naive version, equivalent to the BCS treatment of the transverse spin fluctuations, as well as a holon-spinon version.