Supercurrent in ultrasmall Josephson junctions

G.-L. Ingold and H. Grabert

Physica B 194–196, 1025–1026 (1994) DOI: 10.1016/0921-4526(94)90842-7

In ultrasmall Josephson junctions where the charging energy exceeds the Josephson coupling energy, the usual supercurrent at zero voltage is completely suppressed. However, in the presence of environmental modes, stochastic tunneling of Cooper pairs leads to a current through the junction. For any standard environmental impedances one finds a peak in the current-voltage characteristics near a small voltage proportional to the temperature and the low frequency resistance of the environment. The form of this universal peak, which is independent of the high frequency behavior of the environment, is given analytically. With increasing Josephson coupling the peak merges into the normal supercurrent of a Josephson junction.