Interlayer fluxon interaction in Josephson stacks

Dynamic binding of driven interfaces in coupled ultrathin ferromagnetic layers

We demonstrate experimentally dynamic interface binding in a system consisting of two coupled ferromagnetic layers. While domain walls in each layer have different velocity-field responses, for two broad ranges of the driving field H, walls in the two layers are bound and move at a common velocity. The bound states have their own velocity-field response and arise when the isolated wall velocities in each layer are close, a condition which always occurs as H→0. Several features of the bound states are reproduced using a one-dimensional model, illustrating their general nature.

Shapiro step response in the coherent Josephson flux flow state of Bi2Sr2CaCu2O8+delta

We report the first observation of Shapiro steps in the Josephson flux flow state of Bi2Sr2CaCu2O8+delta stacked junctions. When the junction is irradiated at microwave frequencies in a strong parallel magnetic field ( H> or =1 T), a steep increase of the current is observed in the dc current-voltage characteristics when the external microwave frequency and the Josephson frequency are harmonically related. The existence of Shapiro steps in the Josephson flux flow state is strong evidence of coherent motion of the Josephson vortex lattice through the whole thickness of the stack.