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Break-up of long-range coherence due to phase fluctuations in ultrathin superconducting NbN films | | Y. Noat
; T. Cren
; C. Brun
; F. Debontridder
; V. Cherkez
; K. Ilin
; M. Siegel
; A. Semenov
; H.-W. Hübers
; D. Roditchev
; | | Date: |
15 May 2012 | | Abstract: | Using scanning tunneling spectroscopy (STS), we address the problem of the
superconductor-insulator phase transition (SIT) in homogeneously disordered
ultrathin (2-15 nm) films of NbN. Samples thicker than 8 nm, for which the
Ioffe-Regel parameter $k_F l geq 5.6$, manifest a conventional
superconductivity : A spatially homogeneous BCS-like gap, vanishing at the
critical temperature, and a vortex lattice in magnetic field. Upon thickness
reduction, however, while $k_F l$ lowers, the STS revealed striking deviations
from the BCS scenario, among which a progressive decrease of the coherence peak
height and spatial inhomogeneities. The thinnest film (2.16 nm), while not
being exactly at the SIT ($T_C approx 0.4 T_{C-bulk}$), showed astonishingly
vanishing coherence peaks and the absence of vortices. In the quasi-2D limit,
such clear signatures of the loss of long-range phase coherence strongly
suggest that, at the SIT the superconductivity is destroyed by phase
fluctuations. | | Source: | arXiv, 1205.3408 | | Services: | Forum | Review | PDF | Favorites | |
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