Phase slips and vortex-antivortex pairs in superconducting films with constrictions

A system of two thin coplanar superconducting films seamlessly connected by a bridge is studied. When such a system is cooled, two distinct resistive transitions are observed. The first one is identified with the Berezinskii-Kosterlitz-Thouless (BKT) transition in the film, whereas the second one is a crossover related to the quenching of thermally activated phase slips (TAPS) occurring on the bridge. Using direct and indirect methods, we have measured the resistance R(T ) of such samples over a range of eleven orders of magnitude. Over this broad range of resistance a good agreement is found with the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory of TAPS, which was adopted for short bridges, as given by the simple expression R(T ) = Rn exp [−(c/t)(1 − t)], where t = T/Tc and Rn is the normal resistance of the bridge.