NONDESTRUCTIVE MEASUREMENT OF THE CRITICAL CURRENT AND THE CURRENT-CARRYING LENGTH SCALE IN SUPERCONDUCTING CRYSTALS AND FILMS

In superconductors having a plate-like geometry, valuable information can be obtained from detailed examination of the magnetic hysteresis loop. The length scale LAMBDA on which screening currents flow, and the sheet critical current density K(c) can be evaluated independently. Because of internal weak-links, LAMBDA may be less than the sample dimension, and will change with field and temperature. Experimental results on crystals and films confirming the validity of the analysis are presented.