BLOCH VORTICES IN ONE-DIMENSIONAL JOSEPHSON-JUNCTION ARRAYS

The quantum dynamics of vortices in very long and narrow arrays of Jos ephson junctions have been studied experimentally. The motion of the v ortices through the one-dimensional array is homologous to the motion of a boson through a one-dimensional periodic potential. The external force on the vortices is proportional to the bias current. When the bi as current exceeds a critical value, a negative differential resistanc e is observed. In the presence of external RF radiation the IV-charact eristic exhibits steps at currents which scale with the RF frequency. The position of the steps also depends on the vortex density, which is probably caused by a collective effect of the vortices. These prelimi nary results strongly indicate the existence of a vortex bandstructure .