Optical conductivity of granular aluminum films near the Mott metal-to-insulator transition

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 $2\Delta (0)/k_B{T}_c$ 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 ${\sigma }_{1,s}/{\sigma }_{1,n}$ for all samples up to very high normal state resistivities.

arXiv comment7 pages, 9 figures

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• Tuning the superconducting dome in granular aluminum thin films
• Tunneling study in granular aluminum near the Mott metal-to-insulator transition
• Studies on DC transport and terahertz conductivity of granular molybdenum thin films for microwave radiation detector applications
• Influence of growth parameters on the superconducting transition temperature in granular aluminum films
• Tunneling spectra of unconventional quasi-two-dimensional superconductors