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Enhanced spin pumping into superconductors provides evidence for superconducting pure spin currents

Nature Materials 17, 499–503 (2018) | Download Citation

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Abstract

Unlike conventional spin-singlet Cooper pairs, spin-triplet pairs can carry spin1,2. Triplet supercurrents were discovered in Josephson junctions with metallic ferromagnet spacers, where spin transport can occur only within the ferromagnet and in conjunction with a charge current. Ferromagnetic resonance injects a pure spin current from a precessing ferromagnet into adjacent non-magnetic materials3,4. For spin-singlet pairing, the ferromagnetic resonance spin pumping efficiency decreases below the critical temperature (Tc) of a coupled superconductor5,6. Here we present ferromagnetic resonance experiments in which spin sink layers with strong spin–orbit coupling are added to the superconductor. Our results show that the induced spin currents, rather than being suppressed, are substantially larger in the superconducting state compared with the normal state; although further work is required to establish the details of the spin transport process, we show that this cannot be mediated by quasiparticles and is most likely a triplet pure spin supercurrent.

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Acknowledgements

This work was supported by EPSRC Programme Grant EP/N017242/1.

Author information

Affiliations

  1. Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK

    • Kun-Rok Jeon
    • , Jason W. A. Robinson
    •  & Mark G. Blamire

  2. Cavendish Laboratory, University of Cambridge, Cambridge, UK

    • Kun-Rok Jeon
    • , Chiara Ciccarelli
    •  & Andrew J. Ferguson

  3. London Centre for Nanotechnology and Department of Electronic and Electrical Engineering at University of College London, London, UK

    • Hidekazu Kurebayashi

  4. The Blackett Laboratory, Imperial College London, London, UK

    • Lesley F. Cohen

  5. Department of Physics, Royal Holloway, University of London, Egham, UK

    • Xavier Montiel
    •  & Matthias Eschrig

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Contributions

K.-R.J. and M.G.B. conceived and designed the experiments; the samples were prepared by K.-R.J., with help and the sputtering system provided by J.W.A.R. and M.G.B.; the FMR measurements were carried out by K.-R.J. with the help of C.C., H.K. and A.J.F.; the model calculation was performed by X.M. and M.E. and the data analysis was carried out by K.-R.J., C.C., H.K., J.W.A.R. and M.G.B.; all authors discussed the results and commented on the manuscript, which was written by K.-R.J. and M.G.B.

Competing interests

The authors declare no competing interests.

Corresponding authors

Correspondence to Chiara Ciccarelli or Mark G. Blamire.

Supplementary information

  1. Supplementary Information

    Supplementary text, Supplementary Figures 1–12, Supplementary references

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DOI

https://doi.org/10.1038/s41563-018-0058-9