Order-disorder transition and flow noise for vortices in amorphous films

Abstract

In order to examine the universality of edge contamination (EC) and an order-disorder transition (ODT) for vortex matter reported in NbSe2 single crystals, we measure voltage noise spectra SV (f) induced by current-driven vortices for amorphous MoxGe1-x films with Corbino-disk and striplike geometries. Field dependences of the critical current Ic and SV (f) are nearly independent of contact geometries, indicating that the EC effects are not important on static or dynamic vortex properties in our films. This result is in contrast to what has been reported in NbSe2 crystals. The difference may be attributed to different sample thickness. At 4.1 K, SV at low frequency f exhibits a sharp peak just below the peak field Bp of Ic, suggesting the existence of ODT and metastable vortex states at around Bp. At 5.5 K near the superconducting transition Tc(=6.2 K), however, clear evidence for ODT is not visible.