Interplay between exchange interactions and charging effects in metallic   grains
  We study the effect of the exchange interactions in small superconducting grains near the Coulomb blockade regime. 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. 
Pablo San-Jose, Carlos P. Herrero, Francisco Guinea and Daniel P.   Arovas