Superconductor-insulator transition and the size effect on transport properties observedin ultrathin Y_0.9Pr_0.1Ba₂Cu₃O_y films

Transport properties of ultrathin Y_0.9Pr_0.1Ba₂Cu₃O_y films were studied as a function of thickness and length scale. Samples having planar YBa₂Cu₃O_x-ultrathin Y_0.9Pr_0.1Ba₂Cu₃O_y-YBa₂Cu₃O_x structures were used. The Y_0.9Pr_0.1Ba₂Cu₃O_y channel layer exhibited a superconductor-insulator (SI) transition when the film thickness was below ∼8 nm. The critical sheet conductance of the SI transition was near 4e²h. The sheet conductance of insulator-phase channels shorter than 10 μm was higher than that of 100-μm-long channels with the same thickness due to a size effect. The results suggest that a thickness-dependent correlation length may exist in the insulator-phase Y_0.9Pr_0.1Ba₂Cu₃O_y.