Superconducting and insulating phases of disordered FeSe thin films

The temperature-dependent electronic transport on the superconducting and insulating sides of the superconductor-insulator transition in disordered quasi-two-dimensional textured FeSe thin films is reported. The transition is driven by gradually decreasing the thickness of individual films, thus increasing disorder. In the superconducting phase pronounced resistance tails evolve when the thickness decreases toward the critical thickness of the superconductor-insulator transition. The resistance tails are described reasonably well by the inverse Arrhenius law originally used to account for electronic transport in disordered granular thin films of conventional superconductors below the bulk transition temperature. The transport in the insulating phase is characterized by thermally activated variable range hopping.