Self-Field Limiting of Josephson Tunneling of Superconducting Electron Pairs

The Josephson current that flows at zero potential difference through a barrier between two superconductors is inhibited by external magnetic fields. The self magnetic fields set up by the current itself are shown to have detrimental effects aiso. In a junction whose smallest diameter exceeds a certain penetration distance lambda , the current arises oniy from a fringe of width lambda /sub j/ at the edge of the junction. The magnitude of the maximum current is reduced since the interior does not contribute to the Josephson effect. An estimate of lambda /sub j/is given. (D.C.W.)