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Monochromatic electron emission from the macroscopic quantum state of a superconductor

Nature volume 396, pages 557–559 (1998)Cite this article

Abstract

The ground state of a superconductor is a macroscopic quantum state that can extend coherently over substantial distances1. As a result, electrons tunnelling from two different points (separated by macroscopic length) on the surface of a superconductor remain coherent in phase and so are able to interfere: this property forms the basis of superconducting quantum interference devices (SQUIDs). Another characteristic of electrons tunnelling from a superconductor is that they are monochromatic, their energy being determined by the ground-state energy of the superconducting state. Monochromatic electrons have been observed tunnelling from a superconductor to a normal metal2, and the resulting currents have been used to probe the dynamics of atoms and molecules at interfaces3. Here we report the results of field-emission experiments that confirm the prediction4 that monochromatic electrons can similarly be emitted from a superconductor into vacuum. Monochromatic emissions of this type might find application as the sources in a range of electron-based spectroscopies.

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Figure 1: A schematic diagram of the apparatus used in this experiment.
Figure 2: Typical FE spectra from the Nb tip at 4.2 K and 25 K, which are respectively below and above Tc.
Figure 3: The observed FE spectra from the Nb tip at various temperatures around Tc (= 9.2 K).

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Acknowledgements

We thank N. Osakabe, H. Bergret and T. Sakurai for providing the experimental techniques for the cryo-electron gun, and S. Kurihara for comments concerning the interpretation. This work was supported partly by Special Coordination Funds for Promoting Science and Technology and partly by Research for the Future in JSPS.

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Authors and Affiliations

  1. Department of Applied Physics, Waseda University, 3-4-1, Shinjyuku-ku, Okubo, 169-8555, Tokyo, Japan

    K. Nagaoka, T. Yamashita, S. Uchiyama, M. Yamada, H. Fujii & C. Oshima

  2. Kagami Memorial Laboratory for Material Science and Technologies, Waseda University, 2-8-26, Nishiwaseda, Shinjyuku, 169-0051, Tokyo, Japan

    C. Oshima

Authors
  1. K. Nagaoka
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  2. T. Yamashita
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  3. S. Uchiyama
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  4. M. Yamada
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  5. H. Fujii
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  6. C. Oshima
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Correspondence to C. Oshima.

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Nagaoka, K., Yamashita, T., Uchiyama, S. et al. Monochromatic electron emission from the macroscopic quantum state of a superconductor. Nature 396, 557–559 (1998). https://doi.org/10.1038/25098

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