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Non-quantized penetration of magnetic field in the vortex state of superconductors

Nature volume 407, pages 5557 (07 September 2000) | Download Citation

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Abstract

As first pointed out by Bardeen and Ginzburg in the early sixties1,2, the amount of magnetic flux carried by vortices in superconducting materials depends on their distance from the sample edge, and can be smaller than one flux quantum, φ0 = h/2e (where h is Planck's constant and e is the electronic charge). In bulk superconductors, this reduction of flux becomes negligible at sub-micrometre distances from the edge, but in thin films the effect may survive much farther into the material3,4. But the effect has not been observed experimentally, and it is often assumed that magnetic field enters type II superconductors in units of φ0. Here we measure the amount of flux introduced by individual vortices in a superconducting film, finding that the flux always differs substantially from φ0. We have observed vortices that carry as little as 0.001φ0, as well as ‘negative vortices’, whose penetration leads to the expulsion of magnetic field. We distinguish two phenomena responsible for non-quantized flux penetration: the finite-size effect1,2,3,4 and a nonlinear screening of the magnetic field due to the presence of a surface barrier. The latter effect has not been considered previously, but is likely to cause non-quantized penetration in most cases.

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Acknowledgements

We thank V. Kogan for discussions, and FOM, INTAS and NATO for financial support.

Author information

Affiliations

  1. *University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands

    • A. K. Geim
    • , S. V. Dubonos
    • , I. V. Grigorieva
    •  & K. S. Novoselov
  2. †Department of Physics, The University of Manchester, M13 9PL Manchester, UK

    • A. K. Geim
    •  & I. V. Grigorieva
  3. ‡Institute for Microelectronics Technology , 142432 Chernogolovka, Russia

    • S. V. Dubonos
  4. §Department of Physics, University of Antwerpen (UIA), B-2610 Antwerpen, Belgium

    • F. M. Peeters
    •  & V. A. Schweigert
  5. Institute of Theoretical and Applied Mechanics, 630090 Novosibirsk, Russia

    • V. A. Schweigert

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Correspondence to A. K. Geim.

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https://doi.org/10.1038/35024025

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