Properties of stacked Nb/Al-AlOx/Nb tunnel junctions

Abstract
Successful fabrication of stacked Nb-(Al/AlOx-Nb)n superconducting tunnel junctions with n=3 is reported. Coupling effects are visible in the three measured Fraunhofer patterns of the individual junctions. One of the patterns always shows a considerable field spreading in comparison with the other two patterns, as if the corresponding junction area were much smaller. Negative resistance measured as a function of temperature between 4.2 K and 2 K, in the sum gap region of the I-V characteristics, indicates heating effects.