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.
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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.
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Jeon, KR., 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
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DOI: https://doi.org/10.1038/s41563-018-0058-9
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