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

The current-voltage (I-V) characteristic of disordered superconducting Bi f ilms prepared in situ in a He-3 cryostat by quench deposition has been stud ied. At a fixed temperature, a crossover from linear (Ohmic) to nonlinear ( power-law) behavior was observed as the bias current was increased. An anal ysis of the data based on the theory of dynamic scaling was attempted. A un ique 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 I-V cur ves can be accounted for using a simple picture of current-induced unbindin g of vortex-antivortex pairs that involves a crossover from a logarithmic t o an 1/r interaction between the vortex-antivortex pair. The implications o f such an interaction for the nature of the two-dimensional superconductor- insulator transition are discussed.