Dynamical simulations of fractional giant Shapiro steps in two-dimensional Josephson arrays

We have performed computer simulations of arrays of resistively shunted Josephson junctions in the presence of commensurate magnetic fields and alternating and direct currents. We have found fractional giant Shapiro steps in the simulated current-voltage characteristics in agreement with recent experimental measurements. The detailed motion of the magnetic-field-induced vortices is shown to be in agreement with a previously proposed phenomenological model of Benz et al. [Phys. Rev. Lett. 64, 693 (1990)].