On the suppression of the sidelobes of the supercurrent in small Josephson tunnel junctions

The critical currents of Nb/AI, A1--oxide, AI/Nb tunnel junctions of various shapes have been measured as a function of the applied magnetic field. For the square junction and for some special shapes like the diamond, "1 + cosine" and quartic junctions the Ic (B) pattern falls off theoretically as 1/B ", with n respectively equal to 1, 2, 3 and 4. In general the measurements are in good agreement with the theoretical predictions. For the "1 + cosine" and quartic shapes we found a sidelobe suppression that is even larger than that obtained in theory. For the quartic junction the first sidelobe is only 0.3% of the zero-field current. An It(B) modulation with a small, only slowly decreasing amplitude is observed for the diamond, "1 + cosine", and quartic junctions, that can be explained by rounding of the sharp edges of the junction shapes, due to the fabrication process.