Contact resistance of silver-doped Y-Ba-Cu-O in a magnetic field

The apparent contact resistance at the Ag-particle/superconductor interface in sintered YBa2Cu3O7-δ is found to increase considerably in applied magnetic fields (e.g., by ∼300% at H=200 G, at 77 K). However, in a melt-textured sample where the Ag particles are dispersed within the high Jc grain, no noticeable field dependence of ρc is obtained for H up to 1 T. The field dependence of apparent ρc in fine-grained material is, therefore, attributed mostly to the local current concentration in the superconductor near the Ag particles. It causes Jc to be locally exceeded, with the voltage drop contributing to the apparent ρc value even though the average current density in the superconductor matrix is well below the Jc value. The importance of avoiding local current concentration by proper design and processing of silver contacts, and minimizing low Jc(H) region near the interface, is pointed out