Shapiro step response in the coherent Josephson flux flow state of Bi2Sr2CaCu2O8+δ -: art. no. 247007

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 greater than or equal to 1 T), a steep increase of the current is observed in the de 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.