MAGNETIC-FLUX AND GATE VOLTAGE MODULATION OF THE CURRENT IN A SUPERCONDUCTING LOOP OF ULTRA-SMALL TUNNEL-JUNCTIONS

We have measured the current-voltage (I-V) characteristics of a loop of four superconducting tunnel junctions at low temperatures (T almost-equal-to 50mK). In each branch of the loop, tunneling occurs through a small capacitance island (C(SIGMA) almost-equal-to 1fF). In this geometry we can vary the magnetic flux PHI in the loop and the voltage V(g) on gate electrodes, which have capacitance C(g) to the small islands. We find that both PHI and V(g) modulate the I-V curve.