Tailoring supercurrent confinement in tunable superconducting weak links
Final Report Abstract
In this project, we have studied of the confinement and full control of supercurrent in gate-induced nanostructure based on ultraclean graphene bilayer van der Waals heterostructures. Several experiments have been performed, in both normal and superconducting states. Several systems have been designed, fabricated and probed including electronic interferometers, quantum point contacts and Cooper pair splitters. First, we have shown that supercurrent can fully be controlled, not only in its magnitude, but also in its spatial amplitude using combination of gates to finally obtain full confinement within a one-dimensional constriction. Then, an additional top gate allowed us to fully monitor the created constriction up to the full pinch-off and observe discrete conductance steps in units of 4e2/h in the normal state, demonstrating that confinement does not lift the valley degeneracy in sp2 carbon systems. In such a quantum point contact, we have extensively probed both spin and valley degrees of freedom, showing that, under the first onedimensional subband, quasiparticles undergo anomalous Zeeman splitting due to interaction effects. In another work, we have observed that the opening of a gap in the graphene bilayer electronic band structure, which allows the confinement on charge carriers, undergoes a continuous transition from anti-klein to Klein tunnelling. Using a similar electronic Fabry-Pérot interferometer, we have seen that quasiparticles in graphene superlattice do not follow the usual cyclotron orbit while applying a low magnetic field but counter-intuitive trajectories instead. In a similar cavity, using multiple Andreev reflection, we have seen that the transmission probabilities follow the normal state conductance highlighting the interplay between the Andreev processes and the electronic interferometer. Finally, we have explored the effect of a current injected via normal leads can also control a supercurrent flow and allow the observation of Cooper pair splitting.
Publications
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Tailoring supercurrent confinement in graphene bilayer weak links. Nature Communications, 9(1).
Kraft, Rainer; Mohrmann, Jens; Du, Renjun; Selvasundaram, Pranauv Balaji; Irfan, Muhammad; Kanilmaz, Umut Nefta; Wu, Fan; Beckmann, Detlef; von Löhneysen, Hilbert; Krupke, Ralph; Akhmerov, Anton; Gornyi, Igor & Danneau, Romain
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Tuning Anti-Klein to Klein Tunneling in Bilayer Graphene. Physical Review Letters, 121(12).
Du, Renjun; Liu, Ming-Hao; Mohrmann, Jens; Wu, Fan; Krupke, Ralph; von Löhneysen, Hilbert; Richter, Klaus & Danneau, Romain
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Valley Subband Splitting in Bilayer Graphene Quantum Point Contacts. Physical Review Letters, 121(25).
Kraft, R.; Krainov, I. V.; Gall, V.; Dmitriev, A. P.; Krupke, R.; Gornyi, I. V. & Danneau, R.
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Andreev reflection in ballistic normal metal/graphene/superconductor junctions. Physical Review B, 100(16).
Pandey, P.; Kraft, R.; Krupke, R.; Beckmann, D. & Danneau, R.
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Engineering the Floquet spectrum of superconducting multiterminal quantum dots. Physical Review B, 100(3).
Mélin, Régis; Danneau, Romain; Yang, Kang; Caputo, Jean-Guy & Douçot, Benoît
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Berry phase in superconducting multiterminal quantum dots. Physical Review B, 101(3).
Douçot, Benoît; Danneau, Romain; Yang, Kang; Caputo, Jean-Guy & Mélin, Régis
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Ballistic Graphene Cooper Pair Splitter. Physical Review Letters, 126(14).
Pandey, P.; Danneau, R. & Beckmann, D.
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Critical Current Scaling in Long Diffusive Graphene-Based Josephson Junctions. American Geophysical Union (AGU).
M.T. Haque; M. Will; M. Tomi; P. Pandey; M. Kumar; F. Schmidt; K. Watanabe; T. Taniguchi; R. Danneau; G. Steele & P.J. Hakonen
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Energy distribution controlled ballistic Josephson junction. Physical Review B, 106(21).
Pandey, P.; Beckmann, D. & Danneau, R.
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Spin and valley degrees of freedom in a bilayer graphene quantum point contact: Zeeman splitting and interaction effects. Physical Review Research, 4(2).
Gall, Vanessa; Kraft, Rainer; Gornyi, Igor V. & Danneau, Romain
