Séminaire Nanoélectronique Quantique : Romain Danneau

14h00 // Salle « Remy Lemaire » (K223)

Institut Néel
25 avenue des martyrs - Grenoble

Tailoring supercurrent confinement in graphene bilayer weak links
Romain Danneau (Karlsruhe Institute of Technology Germany)

Graphene appears to be an ideal candidate for superconducting weak link [1-3] thanks to its low contact resistance, large mean free path and its two-dimensionality which allows device geometry flexibility. Designing nanostructures based on electrostatic gating has been at the heart of the research in mesoscopic physics for the last thirty years. While graphene undergoes Klein tunneling making it inappropriate for charge carrier confinement, it is possible to create nanostructures based on band gap engineering in bilayer graphene (BLG). By using edge connected hBN-BLG-hBN heterostructures, we have induced displacement fields between an overall back-gate and a local split-gate, i.e. in a quantum point contact-like structure, to confine the electrons and holes within a 1D constriction. Our superconducting leads allow measuring high supercurrent amplitudes and ballistic interferences. We have studied the confinement of the supercurrent by probing its magnitude and the variations of the magneto-interference patterns while the constriction is formed. We demonstrate that it is possible to fully gate-control both amplitude and density profile a supercurrent, making BLG a highly tunable superconducting weak link. Both analytical and numerical model support our findings. Our work opens up possibilities to create more complex circuits such as superconducting electronic interferometers or transition-edge sensors [3].

References

[1] V.E. Calado, et al., Nat. Nanotech. 10, 761-764 (2015).
[2] M. Ben Shalom, et al., Nat. Phys. 12, 318-322 (2016).
[3] R. Kraft, et al., arXiv : 1702.08773 (2017).

Contact : Romain Danneau

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