Vortex states at T=0 in disordered thin and thick films of a-Mo xSi 1− x

Abstract

We measure the transport properties of highly disordered thin and thick films of amorphous (a-)Mo x Si 1− x at low temperatures T. For thin films we have observed an anomalous peak in the magnetoresistance in fields B higher than the critical field B C of the field-driven superconductor–insulator transition (SIT). This suggests the presence of localized Cooper pairs on the insulating side of the SIT. We present data supporting the view that this insulating regime may correspond to the quantum-vortex-liquid (QVL) phase. The metallic QVL phase in B< B C is not evident, most likely absent. On the other hand, for thick films the existence of the vortex-glass transition and the metallic QVL phase at T=0 has been demonstrated. Based on these data, we construct the T=0 phase diagram of disordered two-dimensional and three-dimensional superconductors.