Abstract
Superconductor-insulator (S-I) transitions tuned by normal tunneling resistance or magnetic field in two-dimensional granular films of tin are investigated, with emphasis on the effect of grain size. We found that for 280 Å grains, the sheet resistance at the S-I boundary in a magnetic field-tunneling resistance plane is close to RQ(≡h⁄4e2), while that for 1200 Å grains is much higher.