Anomalous vortex flow and noise in the quantum liquid phase of amorphous films

We measure the fluctuating component of the flux-flow voltage, δV(t), about the average voltage in the low-temperature (T) liquid phase of amorphous MoxSi1−x films. For the 100-nm-thick film δV(t) originating from the vortex motion is clearly visible in the quantum-vortex-liquid (QVL) phase, where the distribution of δV(t) is asymmetric, suggestive of the unusual vortex motion. For the thin (6 and 4 nm) films, in which the QVL phase is not determined from the T dependence of the resistance, the similar unusual (avalanche-like) vortex motion is observed in nearly the same reduced-T regime. These results support the view that vortex dynamics in the low-T liquid phase of thick and thin films is dominated by common physical mechanisms related to quantum-fluctuation effects.