Fundamental physics of single electron transport

We have studied the critical tunnel resistance for the appearance of the Coulomb blockade in single small-tunnel junctions with electrodes in the normal state and for the phase coherence to appear in the same junctions in the superconducting state. We found that the critical resistances are in accordance with theoretical expectations in both the normal and the superconducting states. For two-dimensional arrays of small junctions, we determined the phase diagram in the parameter space of temperature, Josephson coupling, charging energy and tunnel resistance. It agreed qualitatively with a theoretical diagram based on a competition between charge and vortex Kosterlitz-Thouless transitions.