Coulomb interaction and quantum transport through a coherent scatterer

An interplay between charge discreteness, coherent scattering, and Coulomb interaction yields non-trivial effects in quantum transport. We derive a real-time effective action and an equivalent quantum Langevin equation for an arbitrary coherent scatterer and evaluate its current-voltage characteristics in the presence of interactions. Within our model, at large conductances G(0) and low T (but outside the instanton-dominated regime), the interaction correction to G(0) saturates and causes conductance suppression by a universal factor which depends only on the type of the conductor.