Cutoff length in the logarithmic interaction between a vortex-antivortex pair in quench-condensed superconducting Bi films

The current-voltage (Formula presented) characteristic of disordered superconducting Bi films prepared in situ in a (Formula presented) cryostat by quench deposition has been studied. At a fixed temperature, a crossover from linear (Ohmic) to nonlinear (power-law) behavior was observed as the bias current was increased. An analysis of the data based on the theory of dynamic scaling was attempted. A unique value for the critical exponent is shown to be difficult to determine from the scaling alone. On the other hand, the features seen in the (Formula presented) curves can be accounted for using a simple picture of current-induced unbinding of vortex-antivortex pairs that involves a crossover from a logarithmic to an (Formula presented) interaction between the vortex-antivortex pair. The implications of such an interaction for the nature of the two-dimensional superconductor-insulator transition are discussed.