Coherent States of Two-dimensional Josephson Junction Networks

We have investigated numerically the phase--locking behavior of two-dimensional Josephson junction arrays,taking into account a finite inductance ($l\stackrel{>}{\sim}1$) of the unit cell and external magnetic fields. Within this model we demonstrate the existence of multi--valued {\it I--V} curves of the network. Different branches of the {\it I--V} curve correspond to "in--phase" and "anti--phase" coherent states with high and low levels of output power, respectively. The arrays show remarkable hysteretic transitions between these states under influence of external magnetic fluxes in the range $- \Phi_0/4 < \Phi_{ext} < \Phi_0/4$.