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Quasiparticle-mediated spin Hall effect in a superconductor

Nature Materials volume 14, pages 675–678 (2015)Cite this article

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Abstract

In some materials the competition between superconductivity and magnetism brings about a variety of unique phenomena such as the coexistence of superconductivity and magnetism in heavy-fermion superconductors1 or spin-triplet supercurrent in ferromagnetic Josephson junctions2,3,4. Recent observations of spin–charge separation in a lateral spin valve with a superconductor5,6 evidence that these remarkable properties are applicable to spintronics7, although there are still few works exploring this possibility. Here, we report the experimental observation of the quasiparticle-mediated spin Hall effect in a superconductor, NbN. This compound exhibits the inverse spin Hall (ISH) effect8 even below the superconducting transition temperature. Surprisingly, the ISH signal increases by more than 2,000 times compared with that in the normal state with a decrease of the injected spin current. The effect disappears when the distance between the voltage probes becomes larger than the charge imbalance length9,10, corroborating that the huge ISH signals measured are mediated by quasiparticles.

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Figure 1: Schematic image of spin Hall measurement.
Figure 2: Experimental results of ISHE above TC.
Figure 3: ISHE below TC.
Figure 4: NbN length dependence of the observed signals.

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Acknowledgements

The authors acknowledge helpful discussions with H. Adachi, S. Hikino and Y. Ohnuma. We also would like to thank Y. Iye and S. Katsumoto for the use of the lithography facilities. This work is partly supported by KAKENHI.

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Authors and Affiliations

  1. Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, Japan

    T. Wakamura, Y. Omori, Y. Niimi & Y. Otani

  2. Department of Quantum Engineering, Nagoya University, Nagoya 464-8603, Japan

    H. Akaike & A. Fujimaki

  3. Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

    S. Takahashi

  4. CREST, Japan Science and Technology, Tokyo 102-0075, Japan

    S. Maekawa

  5. Advanced Science Research Center, Japan Atomic Energy Agency, Tokai 319-1195, Japan

    S. Maekawa

  6. RIKEN-CEMS, 2-1 Hirosawa, Wako 351-0198, Japan

    Y. Otani

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  1. T. Wakamura
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Contributions

T.W. and H.A. fabricated samples. T.W. performed measurements. Analyses were done by T.W. and Y.Omori. Manuscript was prepared by T.W., H.A., Y.N., S.T. and Y.Otani. S.T. and S.M. gave theoretical suggestions. This work was supervised by A.F., S.M. and Y.Otani.

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Correspondence to Y. Otani.

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Wakamura, T., Akaike, H., Omori, Y. et al. Quasiparticle-mediated spin Hall effect in a superconductor. Nature Mater 14, 675–678 (2015). https://doi.org/10.1038/nmat4276

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