Anomalous Vortex Motion in the Quantum-Liquid Phase of AmorphousMoxSi1−xFilms

Abstract

We measure, in real time (t), the fluctuating component of the flux-flow voltage V(t), deltaV(t) identical withV(t)-V0, about the average V0 in the vortex-liquid phase of amorphous MoxSi1-x films. For the thick film, deltaV(t) originating from the vortex motion is clearly visible in the quantum-liquid phase, where the distribution of deltaV(t) is asymmetric, indicative of large velocity and/or number fluctuations of driven vortices. For the thin film the similar anomalous vortex motion is observed in nearly the same (reduced-)temperature regime. These results suggest that vortex dynamics in the low-temperature liquid phase of thick and thin films is dominated by common physical mechanisms, presumably related to quantum effects.

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

“…1͑d͔͒. 14 For the a-Mg x B 1−x film the T dependence of in different B and the phase diagram ͓Fig. 1͑e͔͒ obtained from ͑T , B͒ are qualitatively similar to those for the a-Mo x Si 1−x films.…”

“…14 We have suggested that the vortex dynamics in the QVL phase is dominated by quantum fluctuations. However, there is no theory that accounts for the finding comprehensively.…”

“…In measuring V͑t͒ with a time resolution of 390 s and S V ͑f͒ in a frequency range f = 1 Hz-5 kHz, the voltage enhanced with a preamplifier ͑placed at 300 K͒ was recorded and analyzed, using a fast-Fourier transform spectrum analyzer. 14,18 The setup of S V measurement is nearly the same as that used in Ref. 18.…”

“…1͑c͔͒ for the most resistive film 5 studied previously. 14 Here, B g is the vortex-glass ͑VG͒ transition and B c2 ͑0͒ is an upper critical field ͑defined by the 95% criterion͒ at T → 0; 8.77 and 3.43 T for films 1 and 5, respectively.…”

Order–disorder transition and flow noise in an film

“…Our work clearly shows that S V is a very powerful tool to detect the phase transition(s) in the vortex-solid phase [14], where the linear resistance R is always zero, as well as in the liquid phase [16,17], which cannot be detected by ordinary static measurements (e.g., dc voltage V or R). From an experimental point of view, in order to detect such transitions clearly, we must select an appropriate value of V in measuring S V .…”