Mode locking of vortex matter in the peak effect regime of amorphous MoGe films

We have investigated flow properties of vortex matter in the peak effect regime of amorphous MoGe films by a mode locking (ML) technique. While dc current–voltage (I–V) characteristic exhibits a S-shaped anomaly, we observed striking frequency dependence in a ML feature: above a minimum frequency to observe the ML resonance, the maximized ML width increases with frequency and seems to saturate at high frequency. A comparison indicates that the I–V anomaly does not coincide with the onset of ML, but occurs in a velocity range where fractions of mode locked vortices increase rapidly with velocity.