Abstract
We have measured the perpendicular upper critical field, Hc2(T), in ultrathin granular Pb films with normal-state sheet resistances, RN, that range from 10 Ω to 11 kΩ. The films with the highest RN 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 RN=11 kΩ is consistent with the picture that fluctuations in the phase of the order parameter dominate the S-I transition in these films.
Original language | English |
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Pages (from-to) | 14334-14337 |
Number of pages | 4 |
Journal | Physical Review B |
Volume | 47 |
Issue number | 21 |
DOIs | |
State | Published - 1993 |