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Measurement of magnetic penetration depth and superconducting energy gap in very thin epitaxial NbN films
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View: Figures


Image of FIG. 1.
FIG. 1.

(a) Schematic diagram of the coil assembly in our penetration depth measurement setup. The upper (primary) coil has 28 turns with the half closer the film wound in one direction and the farther half wound in the opposite direction. The lower (secondary) has 120 turns wound in the same direction in four layers. (b) Variation of with film thickness for epitaxial NbN thin films. The inset shows and for the thickest and the thinnest film.

Image of FIG. 2.
FIG. 2.

[(a) and (b)] Tunneling conductance spectra normalized at 7 mV for the 50 and 5 nm thick films, respectively. The successive temperatures are (a) 4.7, 5.8, 9.35, 11, 11.8, 12.5, and 13.7 K and (b) 5.2, 6.3, 7.9, 8.8, 9.8, 10.2, and 10.6 K, respectively. The solid lines show the theoretical fits to the spectra. [(c) and (d)] Temperature variation in (●) and (◼) along with the expected BCS behavior for (lines) for the same two films; the insets show the topographic image [ for (c) and for (d)] at 5 K of the surface.

Image of FIG. 3.
FIG. 3.

(a) Temperature variation in for NbN films with different thickness; (b) extracted from tunneling measurements (▲) and penetration depth (△) as a function of ; (c) (◼) and (◆) as a function of ; (d) as a function of .

Image of FIG. 4.
FIG. 4.

Temperature variation in close to for 6.5 and 3 nm films. The dashed lines show the theoretical fit to the data. The best fit parameters are , for the 3 nm sample and , for the 6.5 nm sample. Intersection with the solid line is where the universal KTB, smeared out by inhomogeneities is expected:.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Measurement of magnetic penetration depth and superconducting energy gap in very thin epitaxial NbN films