2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/26902A discrete charge transfer in a small tunnel junction where Coulomb interactions are important can excite electron-hole pairs near the Fermi level. We use a simple model to study the associated nonequilibrium properties and found two novel effects: (i) for junctions with electrodes of the same electronic properties, a leakage current exists within the Coulomb gap even when the environmental impedance is infinite; (ii) for junctions with electrodes of different electronic properties, the differential conductance diverges when a net interaction between conduction electrons is attractive, and it is strongly suppressed for a net repulsive interaction.8 pages (RevTex). Figures upon requestCondensed Mattertext