Scale dependent superconductor–insulator transition

We study the disorder-driven superconductor-to-insulator transition in amorphous films of high carrier-concentration indium-oxide. Using thin films with various sizes and aspect ratios we show that the ‘critical’ sheet-resistance R□ depends systematically on sample geometry; superconductivity disappears when R□ exceeds ≈6 kΩ in large samples. On the other hand, wide and sufficiently short samples of the same batch exhibit superconductivity (judged by conductivity vs. temperature) up to R□ which is considerably larger. These results support the inhomogeneous scenario for the superconductor–insulator transition.