Properties of locally doped bi-crystal grain boundary junctions

A new type of locally doped superconducting weak link has been developed. Fe and Pt were introduced locally in bi-crystal based grain boundaries in YBa2Cu3O7-δ thin films. Pt doping did not influence supercurrent transport noticeably. For Fe doped weak links, a Josephson effect was initially observed but it transformed into a highly resistive, low critical current state after thermal cycling. At that stage, an increased tunneling resistance at low bias and an off-set in voltage at high bias current were observed at temperatures up to 77K. The behavior is interpreted as due to single electron charging effects as narrow superconducting channels across the boundary break up into small metallic particles in an insulating barrier region. (orig.)