Charging energy and phase delocalization in single very small Josephson tunnel junctions

The current-voltage characteristics are measured for very small (0.4-0.02 sq micron) Sn-SnO(x)-Sn tunnel junctions having a charging energy (e squared)/2C comparable to their other characteristic energies. In the higher-Rn devices, after rising just below Te, Ic decreases as the temperature is decreased further, and then increases again at the lowest temperatures. Although the junctions are hysteretic, a significant resistance is found at currents below Ic. An interpretation involving the quantum nature of phi and the competition between the charging, Josephson, and thermal energies of the system is proposed. (Author)