RF POWER DEPENDENCE OF SUBHARMONIC VOLTAGE SPECTRA OF 2-DIMENSIONAL JOSEPHSON-JUNCTION ARRAYS

We have measured the rf-bias-current dependence of the nu/2 subharmonic spectral response of planar 300 X 300 Nb-Au-Nb proximity-coupled Josephson-junction arrays. The nu/2 subharmonic voltage spectrum was examined at two rf-bias frequencies, nu/nu(c) almost-equal-to 1.4, 2.0 (nu(c) almost-equal-to 120 MHz), and in applied magnetic fields corresponding to f=0, 1/2 flux quantum per plaquette. The measurements were compared to analytical predictions for an rf-biased asymmetric superconducting quantum interference device with non-negligble loop inductance and large rf-bias-current amplitudes, based on the resistively shunted Josephson-junction model. Reasonable agreement was found between experiment and theory, suggesting that a possible origin for the observed subharmonic behavior in arrays involves an interplay between array plaquette inductances and junction critical-current variations.