Flux-flow noise driven by quantum fluctuations in a thick amorphous film

We measure the voltage-noise spectrum SV(f) (where f is a frequency) as well as the time (t)-dependent component δV(t) of the flux-flow voltage in the low temperature liquid phase of a thick amorphous MoxSi1−x film. In the quantum-liquid phase both the amplitude ∣δV∣ of voltage fluctuations and the asymmetry of the probability distribution of δV(t) show an anomalous increase; the spectral shape of SV(f) is of a Lorentzian type, suggesting the shot-noise-like vortex motion with a large “vortex-bundle size” and short characteristic time.