Abstract
We have measured the perpendicular upper critical field, (T), in ultrathin granular Pb films with normal-state sheet resistances, , that range from 10 Ω to 11 kΩ. The films with the highest are near the threshold for the superconductor-to-insulator (S-I) transition. We compare our results to calculations for granular superconductors and obtain values for the grain size and coherence length characteristic of a single grain. In addition, we present a measurement of the ratio of the intergrain Josephson-coupling energy to the single-grain condensation energy near the S-I transition in these films. The small value of this ratio, 0.05, at =11 kΩ is consistent with the picture that fluctuations in the phase of the order parameter dominate the S-I transition in these films.
- Received 22 October 1992
DOI:https://doi.org/10.1103/PhysRevB.47.14334
©1993 American Physical Society