CRITICAL CURRENTS IN FRUSTRATED 2-DIMENSIONAL JOSEPHSON ARRAYS

Using the peak in dynamic resistance versus current to indicate the intrinsic critical current Ic0, the magnetic-field dependence of Ic0 in two-dimensional Josephson junction arrays has been inferred from differential resistance measurements at finite voltages. This peak is particularly clear when a magnetic-field-induced vortex superlattice is strongly commensurate with the underlying lattice. At weakly commensurate fields, dV/dI rises sharply at approximately 10% of the zero-field Ic0, in qualitative agreement with the prediction of Lobb et al. [Phys. Rev. B 27, 150 (1983)] for the pinning of isolated vortices. New exact calculations of the critical current are presented for the cases of f=1/2 and 1/3 (f is the average number of flux quanta per cell of the array), which agree well with our experimental measurements. Implications of these exact results for the effect of boundary conditions in computer simulations on small arrays are also noted. © 1990 The American Physical Society.