Abstract
We report measurements of the energy gap of granular aluminum films by THz spectroscopy. We find that as the grains progressively decouple, the coupling ratio 2Δ(0)/kBTc increases above the BCS weak-coupling ratio 3.53, and reaches values consistent with an approach to BCS-BEC crossover for the high-resistivity samples, expected from the short coherence length. The Mattis-Bardeen theory describes remarkably well the behavior of σ1,s/σ1,n for all samples up to very high normal-state resistivities.
Original language | English |
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Article number | 224503 |
Journal | Physical Review B |
Volume | 99 |
Issue number | 22 |
DOIs | |
State | Published - 5 Jun 2019 |
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics