Order-disorder transition of vortex matter ina-MoxGe1−xfilms probed by noise

Abstract

We measure voltage noise spectra ${S}_{V}(f)$ generated by current-driven vortices at various fields $B$ including the peak-effect regime for amorphous ${\text{Mo}}_{x}{\text{Ge}}_{1\ensuremath{-}x}$ films with Corbino-disk and striplike contact geometries. Field dependences of the critical current ${I}_{c}$ and ${S}_{V}(f)$ are nearly independent of contact geometries, indicating that edge effects are not important on static or dynamic vortex properties. This is in contrast to the result reported for ${\text{NbSe}}_{2}$ crystals with much larger thickness. ${S}_{V}(f)$ at low frequency $f$ exhibits a sharp peak just below the peak field ${B}_{p}$ of ${I}_{c}$, where the characteristic time of vortex motion increases significantly. The results suggest the existence of the order-disorder transition and vortex instabilities due to coexisting vortex phases at around ${B}_{p}$.