Amplitude-dependent velocity of vortices in long Josephson junctions estimated from microwave-induced dc voltages

The microwave-induced dc voltage in long Josephson tunnel junctions in the absence of dc bias currents is studied to obtain the velocity of a moving vortex train driven by a microwave. Detailed experiments for the induced dc voltage are carried out for the experimental configuration where the amplitude and the length of the vortex train can be controlled by the magnitudes of the applied microwave and the dc magnetic field. An analysis of the induced dc voltage is made on the basis of Whitham's averaged Lagrangian method, which explains well the observed dependences of the induced dc voltage on the microwave power and the dc magnetic field. The velocity of the vortex train is estimated from the observed dc voltage, and is shown to be strongly dependent on the amplitude as is predicted from the theory.