Electrodynamics of granular aluminum from superconductor to insulator: Observation of collective superconducting modes
- Levy-Bertrand, F.
- Klein, T.
- Grenet, T.
- Dupré, O.
- Benoit, A.
- Bideaud, A.
- Bourrion, O.
- Calvo, M.
- Catalano, A.
- Gomez, A.
- Goupy, J.
- Grünhaupt, L.
- Luepke, U.
- Maleeva, N.
- Valenti, F.
- Pop, M.
- Monfardini, A.
DOIAbstract
International audienceWe report on a detailed study of the optical response and Tc−ρ phase diagram (Tc being the superconducting critical temperature and ρ the normal state resistivity of the film) of granular aluminum, combining transport measurements and a high resolution optical spectroscopy technique. The Tc−ρ phase diagram is discussed as resulting from an interplay between the phase stiffness, the Coulomb repulsion, and the superconducting gap Δ. We provide direct evidence for two different types of well resolved subgap absorptions, at ω1≃Δ and at Δ≲ω2≲2Δ (decreasing with increasing resistivity)
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