Quantum Phenomena in Mesoscopic Superconducting Tunnel Junctions

摘要

We report a low temperature study of very small superconducting tunnel junctions. The samples were fabricated by using electron-beam lithography and thermal evaporation in single-junction, double-junction and eleven-junction-array configurations. The junctions had normal resistances between 0.5 and 140 kilo-ohms and areas between 0.1 and 0.02 sq micrometer. We measured the current-voltage characteristics of the devices at low temperatures (20 mk -4 K), using a dilution refrigerator. In general, the devices had a large single electron charging energy E(c) is identical to sq e /2c of order 1 K. By varying the ratio of Ec to the Josephson coupling energy E(j), we studied the crossover between the conventional Josephson regime, in which E(j)>>E(c), and the Coulomb blockade regime, in which charging effects are dominant. For comparable charging and Josephson energies the I-V curve is resistive at all currents, and exhibits a novel low-voltage resistance R(o) at currents less than the critical current Ic. (RH)