Single electron effects and Bloch oscillations in normal and superconducting tunnel junctions

Abstract We investigate the effect of the single electron charging energy in small capacitance normal and superconducting tunnel junctions. The Coulomb blockade gives rise to various experimentally observable phenomena, e.g. to a “Coulomb gap” in the dc current-voltage characteristic or to ac oscillations of the voltage in response to a dc current (“SET” and Bloch oscillations). We extend previous work of Averin and Likharev to general ratios between the charging energy and the Josephson coupling energy and to arbitrarily strong dissipation. In these regimes macroscopic quantum effects gain increasing importance. Among them are the Zener tunneling and the modification of the energy eigenstates of the Josephson junction by strong dissipation. We discuss the relevance of these effects for the experiments.