Abstract
To study the superconductor-insulator (SI) transition in two-dimensional systems, we measured electrical resistance of Sn granular films with 24 nm grains over a temperature range from 9 K to 50 mK. A distinct SI transition was observed when the normal-conducting sheet resistance R N is increased, showing that neither flat tail nor quasi reentrance is the intrinsic effect in granular systems. If we define R N as the sheet resistance at 77 K, the critical sheet resistance R c for the SI transition exists between 6.0 kΩ and 6.9 kΩ. For the samples which showed superconductivity at low temperatures, we analyzed the resistance based on the vortex Kosterlitz-Thouless (KT) transition. Evaluating from the extrapolation of KT transition temperature T c →0, R c is 6.4 kΩ, which is very close to R Q ≡ h /4 e 2 .
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