Temperature Dependence of Critical Current in Granular Al Bridges with Different Thicknesses and Widths

Critical currents of granular Al bridges with different thicknesses and widths have been measured as a function of temperature. The experimental values of critical current were somewhat smaller than the pair-breaking current in the Ginzburg-Landau theory, being proportional to ( T c - T ) 3/2 near the critical temperature T c . In the lower temperature region they became to be proportional to ( T c - T ). It was found from the temperature and thickness dependences that critical current seems to be governed by the mechanism, different from the pair-breaking one. Slightly below T c , appearance of electrical resistance was observed, depending on the bridge thickness, but not on its width. It is suggested that vortices are thermally activated and their flow generates a voltage.