Exchange interaction as the source of pairing in correlated electron systems: a brief overview

We address the question of real space pairing induced by exchange interaction, customarily associated with the presence of the broken-symmetry magnetism. For such mechanism of pairing, the appearance of superconductivity (or superfluidity) without magnetism presents itself still as a highly nontrivial problem and it seems, it can be practically realized only when the kinetic energy of individual-particle motion is comparable or even smaller than the magnitude of exchange interaction that takes place among strongly correlated fermions, where the kinetic exchange and/or the Hund's rule coupling can become relatively strong in the vicinity of the onset of the Mott insulating state. In that situation, the pairing arises from a coherent correlated pair motion rather than from a free motion of a tightly bound pair. We elaborate on this question in general terms, as well as provide selected results in the mean-field approximation in concrete situations.