Magnetic-field-induced Metallic Phase at Low Temperature in Two-dimensional Superconductors

We measure the resistance R(T) at low temperature T in various fields B for an amorphous (a-)MoxGe1-x thin film with weak disorder (i.e., small normal-state resistance Rn) and weak pinning. We confirm the presence of the intervening metallic phase between superconducting and insulating phases, consistent with earlier work on the a-MoxGe1-x thin film with stronger disorder. The result is in contrast to what has been observed for the a-MoxSi1-x thin films with stronger pinning, in which the B-driven superconductor-insulator transition is clearly visible. We also find that for the a-MoxGe1-x thin films the reduced crossover temperature, below which the activated behavior of R(T) in B changes to the metallic behavior, and field region of the intervening metallic phase are significantly suppressed for the less disordered film. We interpret the results in terms of decreased quantum fluctuation effects due to reduced Rn.