Vortex flow and shot noise in the quantum-liquid phase of thick amorphous superconducting films

We measure the fluctuations (noise) of the vortex-flow voltage in the low-temperature liquid phase of thick amorphous $(a\text{\ensuremath{-}}){\mathrm{Mg}}_{x}{\mathrm{B}}_{1\ensuremath{-}x}$ and $a\text{\ensuremath{-}}{\mathrm{Mo}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x}$ films with different transition temperatures and widths of the quantum-vortex-liquid (QVL) phase. An anomalous vortex flow with an asymmetric distribution of (real-time) voltage fluctuations is commonly observed in the QVL phase, independent of material as well as strength of quantum fluctuations. In the QVL phase we observe the Lorentzian-type noise spectra indicative of shot noise, whose origin is attributed to the vortex bundles that are depinned and pinned randomly in the stationary flow of QVL.

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