DYNAMIC MEASUREMENT OF PERCOLATIVE CRITICAL EXPONENTS IN DISORDERED JOSEPHSON-JUNCTION ARRAYS

The complex conductance G(omega) of site-diluted Josephson junction ar rays close to the percolation threshold was measured over a wide range of frequencies omega. Well below T-c both the superfluid [omega ImG] and dissipative [ReG] components are independent of omega below a crit ical frequency omega(c), whereas G(omega) (proportional to) omega(-u) with u approximate to 1/2 for omega > omega(c). This is shown to refle ct the crossover from a Euclidean regime (omega < omega(c)) dominated by phononlike modes of the phase system to a fractal regime (omega > o mega(c)), where the relevant excitations are localized fractons. Perco lative critical exponents extracted from the data are consistent with theoretical predictions.