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# 4π-periodic Andreev bound states in a Dirac semimetal

## Abstract

Although signatures of superconductivity in Dirac semimetals have been reported, for instance by applying pressure or using point contacts, our understanding of the topological aspects of Dirac semimetal superconductivity is still developing. Here, we utilize nanoscale phase-sensitive junction technology to induce superconductivity in the Dirac semimetal Bi1−xSbx. Our radiofrequency irradiation experiments then reveal a significant contribution of 4π-periodic Andreev bound states to the supercurrent in Nb–Bi0.97Sb0.03–Nb Josephson junctions. The conditions for a substantial 4π contribution to the supercurrent are favourable because of the Dirac cone’s very broad transmission resonances and a measurement frequency faster than the quasiparticle poisoning rate. In addition, we show that a magnetic field applied in the plane of the junction allows tuning of the Josephson junctions from 0 to π regimes. Our results open the technologically appealing avenue of employing the topological bulk properties of Dirac semimetals for topological superconductivity research and topological quantum computer development.

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## Data availability

The data that support the findings of this study are available from the corresponding author on request.

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## Acknowledgements

The authors thank the Diamond Light Source for access to beamline I05 (proposal no. 12969), which contributed to the results presented here, and A. Schiphorst, T. Kim and M. Hoesch for assistance with ARPES experiments. The authors thank R. Lier for numerical calculations. This work was financially supported by the Foundation for Fundamental Research on Matter (FOM), associated with the Netherlands Organization for Scientific Research (NWO), and the European Research Council (ERC) through a Consolidator Grant.

## Author information

Authors

### Contributions

Y.H. made single crystals. C.L. and B.d.R. fabricated devices. C.L, J.C.d.B., B.d.R. and A.d.V. performed transport measurements. C.L., J.C.d.B., B.d.R., A.A.G. and A.B. analysed and modelled transport data. S.V.R., E.v.H. and M.S.G. performed and analysed ARPES measurements. All authors contributed to writing the manuscript.

### Corresponding author

Correspondence to Alexander Brinkman.

## Ethics declarations

### Competing interests

The authors declare no competing interests.

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## Supplementary information

### Supplementary Information

Supplementary Figures 1–16, Supplementary Tables 1–2, Supplementary References 1–26

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Li, C., de Boer, J.C., de Ronde, B. et al. 4π-periodic Andreev bound states in a Dirac semimetal. Nature Mater 17, 875–880 (2018). https://doi.org/10.1038/s41563-018-0158-6

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• DOI: https://doi.org/10.1038/s41563-018-0158-6

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