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Extremely long-range, high-temperature Josephson coupling across a half-metallic ferromagnet

Abstract

The Josephson effect results from the coupling of two superconductors across a spacer such as an insulator, a normal metal or a ferromagnet to yield a phase coherent quantum state. However, in junctions with ferromagnetic spacers, very long-range Josephson effects have remained elusive. Here we demonstrate extremely long-range (micrometric) high-temperature (tens of kelvins) Josephson coupling across the half-metallic manganite La0.7Sr0.3MnO3 combined with the superconducting cuprate YBa2Cu3O7. These planar junctions, in addition to large critical currents, display the hallmarks of Josephson physics, such as critical current oscillations driven by magnetic flux quantization and quantum phase locking effects under microwave excitation (Shapiro steps). The latter display an anomalous doubling of the Josephson frequency predicted by several theories. In addition to its fundamental interest, the marriage between high-temperature, dissipationless quantum coherent transport and full spin polarization brings opportunities for the practical realization of superconducting spintronics, and opens new perspectives for quantum computing.

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Fig. 1: Device structure.
Fig. 2: Superconducting characterization.
Fig. 3: Flux quantization effects.
Fig. 4: The a.c. Josephson effect.

Data availability

The data used in this paper are available from the authors upon reasonable request.

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Acknowledgements

We (J.S., C.L. and N.B.) acknowledge funding from the project Quantox of Quant ERA ERA-NET Cofund in Quantum Technologies (grant agreement no. 731473) implemented within the European Union’s Horizon 2020 programme. Work (J.S., C.L., F.M. and M.G.-H.) was supported by the Spanish AEI through grants MAT2015-72795-EXP, MAT2017-87134-C02 and PID2020-118078RB-I00. J.S. thanks the scholarship programme Alembert funded by the IDEX Paris-Saclay, ANR-11-IDEX-0003-02. Work at CNRS and the Thales lab (J.E.V.) was supported by ERC grant no. 647100 ‘SUSPINTRONICS’; J.E.V., A.I.B. and J.L. thank the French ANR grant ANR-15-CE24-0008-01 ‘SUPERTRONICS’, and J.E.V. and J.S. thank the COST action ‘Nanocohybri’. We (J.S., C.L. and J.-E.V.) acknowledge funding from the Flag ERA ERA-NET To2Dox project. We thank Helmholtz-Zentrum Berlin for the allocation of neutron/synchrotron radiation beamtime. This project received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 730872. J.S. thanks E. Strambini and F. Giazotto for collaboration in the early stages of this project. J.E.V. thanks C. Ulysse and L. Vila for collaboration in related projects. A.I.B. acknowledges support by the Ministry of Science and Higher Education of the Russian Federation within the framework of state funding for the creation and development of the world-class research center ‘Digital Biodesign and Personalized Healthcare’, no. 075-15-2020-926.

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D.S.-M. and F.A.C. grew the samples and performed resistance and critical current measurements. D.S.-M. and S.M. measured angle-dependent transport with contributions from A.S., X.P. and A.B.; D.S.-M., L.M. and S.V. measured X-ray absorption. D.S.-M. and S.M. measured Shapiro steps with the guidance and analysis of C.F.-P., N.B. and J.L.; A.I.B. contributed to the theoretical understanding and modelling. G.O., V.R., J.G.-B., M.R., F.G., J.T., A.R., F.M. and M.G.-H. worked on the sample growth and characterization in different stages of the project. M.C. and J.M.G.-C. performed the microscopy. J.S. designed the overall experiment, and J.E.V. contributed with the design of the Josephson characterization. J.S. and J.E.V. wrote the manuscript with the input and help of J.L., A.I.B., S.M., D.S.-M. and C.L. All authors discussed the results and revised the manuscript.

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Correspondence to Javier E. Villegas or J. Santamaria.

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Supplementary Figs. 1–8 and Discussion on the temperature and barrier thickness dependence of the critical current.

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Sanchez-Manzano, D., Mesoraca, S., Cuellar, F.A. et al. Extremely long-range, high-temperature Josephson coupling across a half-metallic ferromagnet. Nat. Mater. 21, 188–194 (2022). https://doi.org/10.1038/s41563-021-01162-5

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