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

Source: Appl. Phys. Lett. 96, 072509 (2010); doi:10.1063/1.3314308

Published 17 February 2010

KEYWORDS and PACS
Keywords
PACS
  • 74.78.-w
    Superconducting films and low-dimensional structures
  • 74.25.Jb
    Electronic structure of superconductors
  • 74.25.Ha
    Magnetic properties of superconductors
  • 74.20.Fg
    BCS theory of superconductivity and its development
  • 74.40.-n
    Fluctuation phenomena
  • YEAR: 2010
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Anand Kamlapure,1 Mintu Mondal,1 Madhavi Chand,1 Archana Mishra,1,2 John Jesudasan,1 Vivas Bagwe,1 L. Benfatto,3 Vikram Tripathi,1 and Pratap Raychaudhuri1
1Tata Institute of Fundamental Research, Homi Bhabha Rd., Colaba, Mumbai 400005, India
2IIC, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India
3INFM-CNR Statistical Mechanics and Complexity Center, University of Rome “La Sapienza,” P.le A. Moro 5, 00185 Rome, Italy
We report the evolution of the magnetic penetration depth (lambda) and superconducting energy gap (Delta) in epitaxial NbN films with thickness (d) varying between 51–3 nm. With decrease in film thickness Tc and Delta(0) monotonically decreases, whereas lambda(0) monotonically increases. Our results show that while the values of Delta(0) and lambda(0) are well described by Bardeen–Cooper–Schrieffer theory, at elevated temperatures, films with d<=6.5  nm show sudden drop in superfluid density associated with the Kosterlitz–Thouless–Berezinski transition. We discuss the implication of these results on the time response of superconducting bolometers made out of ultrathin NbN films. ©2010 American Institute of Physics
History: Received 1 December 2009; accepted 20 January 2010; published 17 February 2010
Permalink: http://link.aip.org/link/?APPLAB/96/072509/1

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