Electronic transport at low temperature below the field-driven superconductor-insulator transition in thin a-MoxSi1−x films

We have shown so far that thin amorphous (a-)MoxSi1−x films exhibit the field-driven superconductor-insulator transition (SIT) at zero temperature (T = 0), while the existence of a metallic quantum-vortex-liquid at T = 0 has been reported in several thin amorphous films. Here we reexamine the possibility of the metallic phase by measuring the T dependence of resistance R(T) for the thin a-MoxSi1−x films with various transition temperatures Tc0 in fields B below the critical field of the “SIT”. We find that the value of Tc0 dominates R(T) at low T. For films with Tc0 larger than 1.0 K, the activation energy U derived from the slope of the Arrhenius plot of R is constant over the whole T region, while for films with Tc0 < 1.0 K, U exhibits a discontinuous decrease below about 0.1 K; however, U remains constant and positive down to the lowest T. All of the data are consistent with the picture of the field-driven SIT.