Magnetoresistance and vortex states below the 2D superconductor–insulator transition near T=0

Abstract

To study the vortex states below the critical field B c of the superconductor–insulator transition in two dimensions (2D), we measure the magnetoresistance at low perpendicular fields B (< B c) for a thin (4 nm) a-Mo x Si 1− x film. We find that the very small temperature-independent resistance remains at T→0 in finite B below B c. Such resistance is not observed for a thick (100 nm) film as well as for the thin film in parallel fields. These results suggest quantum motion of a small number of vortices (dislocations) in the 2D vortex-glass phase in the presence of the current.