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American Journal of Physics -- February 2012 -- Volume 80, Issue 2, pp. 133

Undergraduate experiment in superconductor point-contact spectroscopy with a Nb/Au junction

Lucas Janson, Matthew Klein, Heather Lewis, Andrew Lucas, Andrew Marantan, and Katherine Luna

Department of Physics, Stanford University, Stanford, California 94305-4045

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We describe an experiment in superconductivity suitable for an advanced undergraduate laboratory. Point-contact spectroscopy is performed by measuring the differential conductance between an electrochemically etched gold tip and a 100-nm thick superconducting niobium film with a transition temperature Tc ≈ 7 K. By fitting the results to Blonder–Tinkham–Klapwijk theory using a finite lifetime of quasiparticles, we obtain a superconducting gap energy Δ ≈ 1.53 meV, a lower bound to the Fermi velocity vF ≥ 3.1 × 107 cm/s, and a BCS coherence length ξ ≈ 43 nm for niobium. These results are in good agreement with previous measurements.

© 2012 American Association of Physics Teachers

ACKNOWLEDGMENTS

The authors would like to thank Karlheinz Merkle and the Stanford Physics Machine Shop for machining much of our apparatus, Weigang Wang for his electronics expertise, Robert Hammond for making our Nb thin film, Rick Pam for maintaining the laboratory, and David Goldhaber-Gordon, Malcolm Beasley, and Alexander Fetter for helpful discussions.

Article Outline

  1. INTRODUCTION
  2. THE BTK MODEL
    1. Solution of the BTK model
    2. Differential conductance
    3. Fitting experimental data to the BTK model
  3. EXPERIMENTAL SETUP
  4. RESULTS
  5. CONCLUSION

KEYWORDS and PACS

Keywords

gold, niobium, physics education, point contact spectroscopy, student experiments, superconducting energy gap, superconducting junction devices, superconducting thin films, type I superconductors

PACS

RELATED DATABASES

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History
Received Sep 2010
Accepted Oct 2011

PUBLICATION DATA

ISSN

0002-9505 (print)  
1943-2909 (online)

Publisher

$abstract.society.value is a Member of CrossRef American Association of Physics Teachers

ARTICLE DATA

Digital Object Identifier
http://dx.doi.org/10.1119/1.3660665

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