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Granularity-induced gapless superconductivity in NbN films: evidence of thermal phase fluctuations

G. Lamura·J. C. Villegier·A. Gauzzi·J. Le Cochec·J. Y. Laval·B. Placais·N. Hadacek·J. Bok
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Abstract

Using a single coil mutual inductance technique, we measure the low temperature dependence of the magnetic penetration depth in superconducting NbN films prepared with similar critical temperatures around 16 K but with different microstructures. Only (100) epitaxial and weakly granular (100) textured films display the characteristic exponential dependence of conventional BCS s-wave superconductors. More granular (111) textured films exhibit a linear dependence, indicating a gapless state in spite of the s-wave gap. This result is quantitatively explained by a model of thermal phase fluctuations favored by the granular structure.

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G. Lamura, J. C. Villegier, A. Gauzzi, J. Le Cochec, J. Y. Laval, B. Placais, N. Hadacek, J. Bok. 2002-01-17. Granularity-induced gapless superconductivity in NbN films: evidence of thermal phase fluctuations. https://doi.org/10.1103/physrevb.65.104507

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