Evidence of spatial inhomogeneity near the onset of magnetically induced insulating state in superconducting thin films

Nonmonotonic differential resistance $(dV∕dI)$ is observed in magnetically induced insulating films, which exhibit apparent superconductor-metal-insulator transitions in the low temperature limit; at low bias currents the nonlinear transport is insulatorlike while at high bias currents it is characteristic of metallic phase. The nonmonotonic $dV∕dI$ may be evidence that the insulating state consists of metallic domains connected by point contacts (insulating gaps) implying that spatial inhomogeneities play a dominant role in determining the nature of the apparent metal-insulator transition.