Interplay between exchange interactions and charging effects in metallic grains

Abstract.We study the effect of strong antiferromagnetic exchange interactions in metallic grains in the Coulomb blockade regime. These interactions can be large in superconducting systems or in metallic antiferromagnetic particles. We extend the standard description of the grain in terms of a single collective variable, the charge and its conjugated phase, to include the spin degree of freedom. The suppression of spin fluctuations enhances the tendency towards Coulomb blockade. The effective charging energy and conductance are calculated numerically in the regime of large grain-lead coupling.