Scale dependent superconductor-insulator transition

Abstract

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 $R_{{\small \square}}$ depends systematically on sample geometry; superconductivity disappears when $R_{{\small \square}}$ exceeds $\approx6 $k$\Omega$ in large samples. On the other hand, wide and sufficiently short samples of the same batch exhibit superconductivity (judged by conductivity versus temperature) up to $R_{{\small \square}}$ which is considerably larger. These results support the inhomogeneous scenario for the superconductor-insulator transition.