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Confining superconductivity, quantized conductance and Zeeman splitting in bilayer graphene - Romain Danneau - Mercredi 5 juin 2019 à 11 h

INSP - Sorbonne Université - 4 place Jussieu - 75005 Paris - Barre 22-32, 2e étage, salle 201

Romain Danneau - Karlsruhe Institute of Technology

Abstract

Graphene appears to be an ideal candidate for superconducting weak links, thanks to its low contact resistance, large mean free path and its two-dimensionality that provides device geometry flexibility. 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 local displacement fields, we are able to confine charge carriers in 1D. Our superconducting leads allow measuring high ballistic supercurrent amplitudes and the study of the supercurrent confinement 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 of the supercurrent, making BLG a highly tunable superconducting weak link. We also demonstrate that by adding a overall top gate, one better controls the 1D constriction and observes four fold degenerate quantized steps down to pinch-off. This shows that both confinement and band structure play a crucial role here.