Maximum Tunneling Supercurrents through Josephson Barriers

The maximum tunneling supercurrent through Josephson barriers as a function of barrier dimensions and external magnetic fields has been investigated experimentally. A versatile sample preparation technique allows a two-dimensional distribution of the tunneling current. The results confirm earlier theoretical predictions qualitatively. At zero applied field the maximum tunneling supercurrent initially increases linearly with the barrier length, then saturates due to self-limiting. At nonzero applied field the maximum tunneling supercurrent decreases linearly with increasing magnetic field. It is shown that this holds also for structures in which the field is generated by crossed-film control supercurrents. The Josephson penetration depth of the samples has been 9–22 μm.