A NEW APPROACH TO THE MAGNETIC MEASUREMENT OF CRITICAL CURRENTS IN SUPERCONDUCTING DISKS AND FILMS

Unlike the situation in zero field, the critical state of a thin superconducting disc at fields large compared with the penetration field has a simple approximate solution. The differential susceptibility as the field is first decreased from its maximum value is a direct measure of the length scale LAMBDA on which screening currents circulate, so that both LAMBDA and the critical current density can be measured independently. If weak links are present, this approach allows their evolution with field and temperature to be followed.