Sidelobes suppression in normal-distribution-shaped Josephson tunnel junctions

We have studied normal-distribution-shaped Josephson tunnel junctions for STJ (superconducting tunnel junction) photon detector applications. By employing a normal-distribution function to the shape of the superconducting electrodes sidelobes of the Josephson current were entirely suppressed with a small magnetic field. This behavior was confirmed experimentally by using Nb/AlO/sub x//Nb Josephson tunnel junctions. There were no oscillatory sidelobes in the Josephson current dependence on the magnetic field. Experimental results were in good agreement with theoretical ones. The Josephson current was efficiently suppressed by an external magnetic field of about 0.5 mT at 4.2 K, which is less than one tenth that of other shaped junctions. In the experiment at 0.3 K, Fiske steps due to the resonances were not observed by suppression with a magnetic field of about 1 mT.