Dynamical Phase Transition in a Fully Frustrated Square Josephson Array

We study dynamical phase transitions at temperature T = 0 in a fully frustrated square Josephson junction array subject to a driving current density which has nonzero components parallel to both axes of the lattice. Our numerical results show clear evidence for three dynamical phases: a pinned vortex lattice characterized by zero time-averaged voltages, a ``plastic'' phase in which both voltages are nonzero, and a moving lattice phase in which only one of the time-average voltage components is nonzero. The last of these has a finite transverse critical current.