Conductance quantization, supercurrent and multiple Andreev reflection in bilayer graphene quantum point contacts

By using local displacement fields in bilayer graphene (BLG), it is possible to elec- trostatically confine charge carriers. Connecting superconducting leads to a graphene nanostructure allows to induce high ballistic supercurrent. 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 [1]. Adding an additional overall top gate, one better controls the 1D constriction and observes four fold degen- erate quantized conductance down to full pinch-off [2]. We show that this ballistic effect is also reflected in the supercurrent and in the multiple Andreev reflection as the number of discrete channels is reduced [3].
[1] R. Kraft, J. Mohrmann, R. Du, P.B. Selvasundaram, M. Irfan, U.N. Kanilmaz,
F. Wu, D. Beckmann, H.v. L¨ohneysen, R. Krupke, A. Akhmerov, I. Gornyi & R. Danneau. Nat. Commun. 9, 1722 (2018).
[2] R. Kraft, I.V. Krainov, V. Gall, A.P. Dimitriev, R. Krupke, I.V. Gornyi & R. Danneau. Phys. Rev. Lett. 121, 257703 (2018).
[3] R. Kraft, R. M´elin, R. Krupke, B. Douc¸ot & R. Danneau. Unpublished