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Renormalization of the Coulomb blockade gap due to extended tunneling in nanoscopic junctions

In this work we discuss the combined effects of finite-range electron-electron interaction and finite-range tunneling on the transport properties of ultrasmall tunnel junctions. We show that the Coulomb blockade phenomenon is deeply influenced by the interplay between the geometry and the screening properties of the contacts. In particular if the interaction range is smaller than the size of the tunneling region a "weakly correlated" regime emerges in which the Coulomb blockade gap $\D$ is significantly reduced. In this regime $\D$ is not simply given by the conventional charging energy of the junction, since it is strongly renormalized by the energy that electrons need to tunnel over the extended contact.