Suppression of the Vortex-Glass Phase in Quasi-2D a-MoxSi1−x Films

We study the effects of reduced dimensionality on the vortex phase diagram based on the measurements of ac complex resistivity for amorphous Mo x Si 1-x films. As the film thickness decreases, the (normalized) vortex-glass-transition (VGT) line is suppressed, while the (normalized) upper-critical-field line stays almost unchanged. The trend for the vortex-liquid phase to increase with decreasing film thickness is in accordance with the VG theory. The (relative) width of the liquid phase at low temperatures is wider for the thinner film. This result is consistent with a view that the quantum-vortex-liquid phase is driven by strong quantum fluctuations, which are enhanced with decreasing dimensionality.