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Extremely long quasiparticle spin lifetimes in superconducting aluminium using MgO tunnel spin injectors

Abstract

There has been an intense search in recent years for long-lived spin-polarized carriers for spintronic and quantum-computing devices. Here we report that spin-polarized quasiparticles in superconducting aluminium layers have surprisingly long spin lifetimes, nearly a million times longer than in their normal state. The lifetime is determined from the suppression of the aluminium’s superconductivity resulting from the accumulation of spin-polarized carriers in the aluminium layer using tunnel spin injectors. A Hanle effect, observed in the presence of small in-plane orthogonal fields, is shown to be quantitatively consistent with the presence of long-lived spin-polarized quasiparticles. Our experiments show that the superconducting state can be significantly modified by small electric currents, much smaller than the critical current, which is potentially useful for devices involving superconducting qubits.

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Figure 1: Experimental conductance and TMR data and comparison with model.
Figure 2: Schematic diagram of superconducting gap suppression and spin accumulation in a DTJ composed of two ferromagnetic electrodes and a superconducting middle electrode.
Figure 3: Modelling of experimental data to determine spin lifetime in the superconducting Al layer.
Figure 4: Tunnel-barrier-thickness dependence of TMR.
Figure 5: Observation of the Hanle effect in F–I–SC–I–F.

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Acknowledgements

We would like to thank B. J. van Wees for useful discussions. This work is partially supported by DMEA, CREST-JST, Grant-in-Aid for Scientific Research from MEXT and the Next Generation Supercomputer Project, Nanoscience program, MEXT, Japan.

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Contributions

H.Y. and S.S.P.P. initiated this work. H.Y. carried out the electrical transport experiments. S-H.Y. grew the samples, and carried out the Hanle effect experiment and the numerical calculations. S.T. and S.M. developed the theoretical models. S.S.P.P. supervised and led this research project. All authors wrote, edited the paper and discussed the data and the results.

Corresponding author

Correspondence to Stuart S. P. Parkin.

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The authors declare no competing financial interests.

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Yang, H., Yang, SH., Takahashi, S. et al. Extremely long quasiparticle spin lifetimes in superconducting aluminium using MgO tunnel spin injectors. Nature Mater 9, 586–593 (2010). https://doi.org/10.1038/nmat2781

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