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

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.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Principle of the approach.
Fig. 2: Enhanced spin transport in the superconducting state when coupled to a strong spin sink.
Fig. 3: Enhanced spin transport in the superconducting state enabled by SOC along with precessing magnetization.

References

  1. 1.

    Linder, J. & Robinson, J. W. A. Superconducting spintronics. Nat. Phys. 11, 307–315 (2015).

    Article  Google Scholar 

  2. 2.

    Eschrig, M. Spin-polarized supercurrents for spintronics: a review of current progress. Rep. Prog. Phys. 78, 104501 (2015).

    Article  Google Scholar 

  3. 3.

    Tserkovnyak, Y., Brataas, A., Bauer, G. E. W. & Halperin, B. I. Nonlocal magnetization dynamics in ferromagnetic heterostructures. Rev. Mod. Phys. 77, 1375–1421 (2005).

    Article  Google Scholar 

  4. 4.

    Ando, K. et al. Inverse spin-Hall effect induced by spin pumping in metallic system. J. Appl. Phys. 109, 103913 (2011).

    Article  Google Scholar 

  5. 5.

    Bell, C., Milikisyants, S., Huber, M. & Aarts, J. Spin dynamics in a superconductor–ferromagnet proximity system. Phys. Rev. Lett. 100, 047002 (2008).

    Article  Google Scholar 

  6. 6.

    Morten, J. P., Brataas, A., Bauer, G. E. W., Belzig, W. & Tserkovnyak, Y. Proximity-effect-assisted decay of spin currents in superconductors. Europhys. Lett. 84, 57008 (2008).

    Article  Google Scholar 

  7. 7.

    Beckmann, D. Spin manipulation in nanoscale superconductors. J. Phys. Condens. Matter 28, 163001 (2016).

    Article  Google Scholar 

  8. 8.

    Hübler, F., Wolf, M. J., Beckmann, D. & Löhneysen, H. v. Long-range spin-polarized quasiparticle transport in mesoscopic Al superconductors with a Zeeman splitting. Phys. Rev. Lett. 109, 207001 (2012).

    Article  Google Scholar 

  9. 9.

    Quay, C. H. L., Chevallier, D., Bena, C. & Aprili, M. Spin imbalance and spin-charge separation in a mesoscopic superconductor. Nat. Phys. 9, 84–88 (2013).

    Article  Google Scholar 

  10. 10.

    Wakamura, T., Hasegawa, N., Ohnishi, K., Niimi, Y. & Otani, Y. Spin injection into a superconductor with strong spin–orbit coupling. Phys. Rev. Lett. 112, 036602 (2014).

    Article  Google Scholar 

  11. 11.

    Yang, H., Yang, S.-H., Takahashi, S., Maekawa, S. & Parkin, S. S. P. Extremely long quasiparticle spin lifetimes in superconducting aluminium using MgO tunnel spin injectors. Nat. Mater. 9, 586–593 (2010).

    Article  Google Scholar 

  12. 12.

    Poli, N. et al. Spin injection and relaxation in a mesoscopic superconductor. Phys. Rev. Lett. 100, 136601 (2008).

    Article  Google Scholar 

  13. 13.

    Wakamura, T. et al. Quasiparticle-mediated spin Hall effect in a superconductor. Nat. Mater. 14, 675–678 (2015).

    Article  Google Scholar 

  14. 14.

    Inoue, M., Ichioka, M. & Adachi, H. Spin pumping into superconductors: A new probe of spin dynamics in a superconducting thin film. Phys. Rev. B 96, 024414 (2017).

    Article  Google Scholar 

  15. 15.

    Rojas-Sanchez, J. C. et al. Spin pumping and inverse spin Hall effect in platinum: the essential role of spin-memory loss at metallic interfaces. Phys. Rev. Lett. 112, 106602 (2014).

    Article  Google Scholar 

  16. 16.

    Gu, J. Y., Caballero, J. A., Slater, R. D., Loloee, R. & Pratt, W. P. Direct measurement of quasiparticle evanescent waves in a dirty superconductor. Phys. Rev. B 66, 140507 (2002).

    Article  Google Scholar 

  17. 17.

    Brataas, A., Nazarov, Y. V. & Bauer, G. E. W. Finite-element theory of transport in ferromagnet–normal metal systems. Phys. Rev. Lett. 84, 2481–2484 (2000).

    Article  Google Scholar 

  18. 18.

    Zhang, W., Han, W., Jiang, X., Yang, S.-H. & Parkin, S. S. P. Role of transparency of platinum–ferromagnet interfaces in determining the intrinsic magnitude of the spin Hall effect. Nat. Phys. 11, 496–502 (2015).

    Article  Google Scholar 

  19. 19.

    Villamor, E., Isasa, M., Hueso, L. E. & Casanova, F. Temperature dependence of spin polarization in ferromagnetic metals using lateral spin valves. Phys. Rev. B 88, 184411 (2013).

    Article  Google Scholar 

  20. 20.

    Flokstra, M. G. et al. Remotely induced magnetism in a normal metal using a superconducting spin-valve. Nat. Phys. 12, 57–61 (2016).

    Article  Google Scholar 

  21. 21.

    Ruggiero, S. T., Track, E. K., Prober, D. E., Arnold, G. B. & DeWeert, M. J. Electron tunneling in tantalum surface layers on niobium. Phys. Rev. B 34, 217–225 (1986).

    Article  Google Scholar 

  22. 22.

    Bell, C. et al. Proximity and Josephson effects in superconductor/antiferromagnetic Nb/gamma-Fe50Mn5 0 heterostructures. Phys. Rev. B 69, 109903 (2003).

    Article  Google Scholar 

  23. 23.

    Grein, R., Löfwander, T. & Eschrig, M. Inverse proximity effect and influence of disorder on triplet supercurrents in strongly spin-polarized ferromagnets. Phys. Rev. B 88, 054502 (2013).

    Article  Google Scholar 

  24. 24.

    Kalcheim, Y., Millo, O., Di Bernardo, A., Pal, A. & Robinson, J. W. A. Inverse proximity effect at superconductor-ferromagnet interfaces: Evidence for induced triplet pairing in the superconductor. Phys. Rev. B 92, 060501(R) (2015).

    Article  Google Scholar 

  25. 25.

    Di Bernardo, A. et al. Signature of magnetic-dependent gapless odd frequency states at superconductor/ferromagnet interfaces. Nat. Commun. 6, 8053 (2015).

    Article  Google Scholar 

  26. 26.

    Bergeret, F. S. & Tokatly, I. V. Spin–orbit coupling as a source of long-range triplet proximity effect in superconductor–ferromagnet hybrid structures. Phys. Rev. B 89, 134517 (2014).

    Article  Google Scholar 

  27. 27.

    Jacobsen, S. H., Kulagina, I. & Linder, J. Controlling superconducting spin flow with spin-flip immunity using a single homogeneous ferromagnet. Sci. Rep. 6, 23926 (2016).

    Article  Google Scholar 

  28. 28.

    Houzet, M. Ferromagnetic Josephson junction with precessing magnetization. Phys. Rev. Lett. 101, 057009 (2008).

    Article  Google Scholar 

  29. 29.

    Holmqvist, C., Teber, S. & Fogelström, M. Nonequilibrium effects in a Josephson junction coupled to a precessing spin. Phys. Rev. B 83, 104521 (2011).

    Article  Google Scholar 

  30. 30.

    König, R., Schindler, A. & Herrmannsdörfer, T. Superconductivity of compacted platinum powder at very low temperatures. Phys. Rev. Lett. 82, 4528–4531 (1999).

    Article  Google Scholar 

  31. 31.

    Tanaka, T. et al. Intrinsic spin Hall effect and orbital Hall effect in 4d and 5d transition metals. Phys. Rev. B 77, 165117 (2008).

    Article  Google Scholar 

  32. 32.

    Gubin, A. I., Il’in, K. S., Vitusevich, S. A., Siegel, M. & Klein, N. Dependence of magnetic penetration depth on the thickness of superconducting Nb thin films. Phys. Rev. B 72, 064503 (2005).

    Article  Google Scholar 

Download references

Acknowledgements

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

Author information

Affiliations

Authors

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.

Corresponding authors

Correspondence to Chiara Ciccarelli or Mark G. Blamire.

Ethics declarations

Competing interests

The authors declare no competing interests.

Supplementary information

Supplementary Information

Supplementary text, Supplementary Figures 1–12, Supplementary references

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Jeon, K., Ciccarelli, C., Ferguson, A.J. et al. Enhanced spin pumping into superconductors provides evidence for superconducting pure spin currents. Nature Mater 17, 499–503 (2018). https://doi.org/10.1038/s41563-018-0058-9

Download citation

Further reading

Search

Quick links

Sign up for the Nature Briefing newsletter for a daily update on COVID-19 science.
Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing