Critical Currents of Superconducting Wide Bridges

The temperature T and perpendicular magnetic field H dependences of the critical current I c have been measured for superconducting wide bridges made of granular aluminum. The measured T dependence of I c near the transition temperature T c deviates from that derived from the Ginzburg-Landau (GL) equations in a uniform current distribution. The deviation occurs even under the condition that the self-magnetic field due to the current is negligible, and it increases as the width of bridge or the coherence length increases. These results show that the pair-breaking current density j c at the edge of bridge is enhanced from j c GL owing to current concentration due to its geometry. The peak structure with clear hysteresis for the sweep of H was observed in the I c - H characteristics. The width of the peak seems to be inversely proportional to the bridge width.