Skip to main content
SpringerLink
Log in

Optical and Tunneling Studies of Energy Gap in Superconducting Niobium Nitride Films

  • Published:
Journal of Low Temperature Physics Aims and scope Submit manuscript

Abstract

We have prepared an epitaxial niobium nitride (NbN) film and NbN/AlN/NbN tunnel junctions to investigate the energy gaps. By measuring the optical conductivity spectrum of a 41-nm-thick film with the critical temperature (TC) of about 14 K by terahertz time-domain spectroscopy, we obtained the gap frequency of about 1.2 THz. An ill-defined gap was suggested due to the broadening of the onset of absorption as the temperature increases. On the other hand, the current–voltage curve measurement of the tunnel junctions showed the current rise at the gap voltage of 5.6 mV (corresponding to 1.4 THz) with a smeared shape as the temperature increases. We found that both gap broadenings can be explained by introducing a temperature-dependent imaginary energy gap part into the superconducting energy gap, corresponding to a finite quasi-particle lifetime in the NbN films.

This is a preview of subscription content, log in via an institution to check access.

Access this article

Log in via an institution

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5

Similar content being viewed by others

References

  1. Z. Wang et al., J. Appl. Phys. 79, 7837 (1996)

    Article  ADS  Google Scholar 

  2. Z. Wang et al., Appl. Phys. Lett. 70, 114 (1997)

    Article  ADS  Google Scholar 

  3. Z. Wang et al., Appl. Phys. Lett. 102, 142604 (2013)

    Article  ADS  Google Scholar 

  4. Y. Uzawa et al., Appl. Phys. Lett. 73, 680 (1998)

    Article  ADS  Google Scholar 

  5. T. Kojima et al., IEEE Trans. Appl. Supercond. 19, 405 (2009)

    Article  ADS  Google Scholar 

  6. Y. Uzawa et al., IEEE Trans. Appl. Supercond. 27, 1500705 (2017)

    Article  Google Scholar 

  7. W. Qiu et al., IEEE Trans. Appl. Supercond. 21, 135 (2011)

    Article  ADS  Google Scholar 

  8. Y. Uzawa et al., Physica C 494, 189 (2013)

    Article  ADS  Google Scholar 

  9. D.C. Mattis, J. Bardeen, Phys. Rev. 111, 412 (1958)

    Article  ADS  Google Scholar 

  10. D. Karecki et al., Phys. Rev. B 25, 1565 (1982)

    Article  ADS  Google Scholar 

  11. B. Mitrovic, L.A. Rozema, J. Phys. Condens. Matter 20, 015215 (2008)

    Article  ADS  Google Scholar 

  12. T. Noguchi et al., Physica C 469, 1585 (2009)

    Article  ADS  Google Scholar 

  13. T. Guruswamy, Ph.D. thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277214

  14. T.-M. Shen et al., Appl. Phys. Lett. 36, 777 (1980)

    Article  ADS  Google Scholar 

  15. Y. Uzawa et al., J. Low Temp. Phys. 193, 512 (2018)

    Article  ADS  Google Scholar 

Download references

Acknowledgements

This work was supported by JSPS KAKENHI Grant Numbers 18H03881 and 19H02205.

Author information

Authors and Affiliations

  1. National Astronomical Observatory of Japan, Mitaka, Japan

    Yoshinori Uzawa & Takafumi Kojima

  2. National Institute of Information and Communications Technology, Koganei, Japan

    Shingo Saito & Wei Qiu

  3. National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan

    Kazumasa Makise

  4. Shanghai Institute of Microsystem and Information Technology, Shanghai, China

    Zhen Wang

Authors
  1. Yoshinori Uzawa
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Shingo Saito
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Wei Qiu
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Kazumasa Makise
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Takafumi Kojima
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Zhen Wang
    View author publications

    You can also search for this author in PubMed Google Scholar

Corresponding author

Correspondence to Yoshinori Uzawa.

Additional information

Publisher's Note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Uzawa, Y., Saito, S., Qiu, W. et al. Optical and Tunneling Studies of Energy Gap in Superconducting Niobium Nitride Films. J Low Temp Phys 199, 143–148 (2020). https://doi.org/10.1007/s10909-019-02324-1

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1007/s10909-019-02324-1

Keywords

Search

Navigation