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

Abstract We measure the fluctuating component of the flux-flow voltage, δ V ( t ), about the average voltage in the low-temperature ( T ) liquid phase of amorphous Mo x Si 1− x films. For the 100-nm-thick film δ V ( t ) originating from the vortex motion is clearly visible in the quantum-vortex-liquid (QVL) phase, where the distribution of δ V ( 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.