Ballistic Josephson junctions in edge-contacted graphene

• Published in: Nature nanotechnology Vol. 10; no. 9; pp. 761 - 764
• Main Authors: Calado, V. E., Goswami, S., Nanda, G., Diez, M., Akhmerov, A. R., Watanabe, K., Taniguchi, T., Klapwijk, T. M., Vandersypen, L. M. K.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.09.2015; Nature Publishing Group
• Subjects: 639/301/119/1003; 639/766/119/1003; 639/925/918/1052; Boron; Carrier density; Graphene; Graphical user interface; Josephson junctions; letter; Magnetic fields; Materials Science; Molybdenum; Nanotechnology; Nanotechnology and Microengineering; Rhenium; Superconductivity; Superconductors; Transport
• ISSN: 1748-3387; 1748-3395
• DOI: 10.1038/nnano.2015.156

Heterostructures of graphene and a superconducting metal allow Josephson junctions to be studied in a regime characterized by ballistic transport. Hybrid graphene–superconductor devices have attracted much attention since the early days of graphene research 1 , 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 contacts 19 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 nitride 19 , 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.