Transparency of Planar Interfaces in Superconductors: A Critical-State Analysis

The problem of determining the transparency of current flow through a planar interface connecting two superconducting parts, being bulks, tapes, or films, is analyzed within the critical-state model. An exact relation between the magnetic moment of a sample containing such an interface and its transparency is derived for rectangular specimens in fully developed Bean critical states. The result can serve as theoretical basis for using standard magnetometry to measure the quality of joints, grain boundaries, and other weak links between superconducting parts.