RF responses and in-phase Josephson vortex motion in an intrinsic Josephson junction system with a periodic pinning potential

We investigate experimentally the dynamics of Josephson vortices interacting with electromagnetic waves in Bi₂Sr₂CaCu ₂O_8+y intrinsic Josephson junction stacks by means of millimeter wave irradiation and numerical simulations based on coupled sine-Gordon equations. We have found that an introduction of pancake vortices by tilting the external magnetic field from CuO₂ planes reveals Shapiro-step-like features on the flux-flow characteristics. Those steps are assumed to be a manifestation of an in-phase coherent motion of Josephson vortices caused by a periodic potential developed by pancake vortices. The results of the numerical simulation, taking into account the periodic potential, supports the validity of such an assumption.