Details

Autor(en) / Beteiligte

• Noat, Y.
• Cherkez, V.
• Brun, C.
• Cren, T.
• Carbillet, C.
• Debontridder, F.
• Ilin, K.
• Siegel, M.
• Semenov, A.
• Hübers, H.-W.
• Roditchev, D.

Titel

Unconventional superconductivity in ultrathin superconducting NbN films studied by scanning tunneling spectroscopy

Ist Teil von

• Physical review. B, Condensed matter and materials physics, 2013-07, Vol.88 (1), Article 014503

Ort / Verlag

American Physical Society

Erscheinungsjahr

2013

Quelle

PROLA - Physical Review Online Archive

Beschreibungen/Notizen

• Using scanning tunneling spectroscopy, we address the problem of the superconductor-insulator phase transition in homogeneously disordered ultrathin (2-15 nm) films of NbN. Samples thicker than 8 nm, for which the loffe-Regel parameter k sub(F)l > or = 5.6, manifest a conventional superconductivity: a spatially homogeneous BCS-like gap, vanishing at the critical temperature, and a disordered vortex lattice in magnetic field. Upon thickness reduction, however, while k sub(F)l lowers, the STS reveals striking deviations from the BCS scenario, among which a progressive decrease of the coherence peak height and small spatial inhomogeneities. In addition, the gap below T sub(C) develops on a spectral background, which becomes more and more "V-shaped" approaching the localization. The thinnest film (2.16 nm), while not being exactly at the superconductor-insulator transition (SIT) (ProQuest: Formulae and/or non-USASCII text omitted), showed unconventional signatures such as the vanishing of the coherence peaks and the absence of vortices. This behavior suggests a weakening of long-range phase coherence, when approaching the SIT in this quasi-2D limit.