Mode locking and noise of driven vortices near the peak-effect regime

We present the measurements of broadband voltage noise generated by the driven vortices near the peak-effect regime of a thick amorphous MoxGe1−x film. We focus on a change in voltage noise as the vortex system undergoes mode locking (ML), which is a dynamic resonance between the ac drive superimposed on the dc drive and lattice-oscillation modes excited collectively. By sweeping the dc current I at fixed ac drive, we find the step-like structure in the current-voltage (I-V) characteristics indicative of ML. At high frequencies f (but well below the ac-drive frequency) the noise spectrum is f-independent. We find a trend for the amplitude of noise (at high f) to decrease in the ML step.