Kink Propagation in a Highly Discrete System: Observation of Phase Locking to Linear Waves

We report the first observation of phase locking between a kink propagating in a highly discrete system and the linear waves excited in its wake. The current-voltage ($I-V$) characteristics of discrete rings of Josephson junctions have been measured. Resonant steps appear in the $I-V$ curve, due to phase locking between a propagating vortex and its induced radiation. Unexpectedly, mode numbers outside the first Brillouin zone are physically relevant, due to the nonlinearity of the system.