Superconductivity near the mobility edge

We study the low-temperature transport properties of amorphous indium oxide films as a function of disorder near the metal-insulator transition. Deep in the insulating regime, the conductivity shows simple variable-range hopping that turns into an Arrhenius activation as the transition is approached. With further decrease in static disorder, superconductivity sets in and the transition temperature increases towards a value of ≊3.3 K. The transition between a superconducting phase and an insulating one is also accompanied by a sign and anisotropy change in the magnetoresistance of the films. These results are discussed in light of recent theories.