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# Ballistic Josephson junctions in edge-contacted graphene

## Abstract

Hybrid graphene–superconductor devices have attracted much attention since the early days of graphene research1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18. So far, these studies have been limited to the case of diffusive transport through graphene with poorly defined and modest-quality graphene/superconductor interfaces, usually combined with small critical magnetic fields of the superconducting electrodes. Here, we report graphene-based Josephson junctions with one-dimensional edge contacts19 of molybdenum rhenium. The contacts exhibit a well-defined, transparent interface to the graphene, have a critical magnetic field of 8 T at 4 K, and the graphene has a high quality due to its encapsulation in hexagonal boron nitride19,20. This allows us to study and exploit graphene Josephson junctions in a new regime, characterized by ballistic transport. We find that the critical current oscillates with the carrier density due to phase-coherent interference of the electrons and holes that carry the supercurrent caused by the formation of a Fabry–Pérot cavity. Furthermore, relatively large supercurrents are observed over unprecedented long distances of up to 1.5 μm. Finally, in the quantum Hall regime we observe broken symmetry states while the contacts remain superconducting. These achievements open up new avenues to exploit the Dirac nature of graphene in interaction with the superconducting state.

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## Acknowledgements

The authors thank V. Singh for sharing the MoRe sputtering recipe and C. Beenakker for discussions. The authors acknowledge support from the EC-FET Graphene Flagship, from the European Research Council (advanced grant no. 339306; METIQUM), from a European Research Council Synergy grant (QC-LAB) and from the Ministry of Education and Science of the Russian Federation (contract no. 14.B25.31.0007). This work is part of the Nanofront Consortium, funded by the Dutch Science Foundation OCW/NWO/FOM.

## Author information

Authors

### Contributions

K.W. and T.T. grew the hBN crystals, G.N. fabricated the devices, V.E.C. and S.G. performed the measurements, and M.D. and A.R.A. carried out the numerical simulations and theory. The measurements were analysed and interpreted by V.E.C., S.G., M.D., A.R.A., T.M.K. and L.M.K.V. The manuscript was written by V.E.C., S.G. and L.M.K.V., with input from A.R.A., M.D. and T.M.K.

### Corresponding author

Correspondence to L. M. K. Vandersypen.

## Ethics declarations

### Competing interests

The authors declare no competing financial interests.

## Supplementary information

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Calado, V., Goswami, S., Nanda, G. et al. Ballistic Josephson junctions in edge-contacted graphene. Nature Nanotech 10, 761–764 (2015). https://doi.org/10.1038/nnano.2015.156

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• DOI: https://doi.org/10.1038/nnano.2015.156

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