Abstract
Quantum dots defined in carbon nanotubes are a platform for both basic scientific studies1,2,3,4,5 and research into new device applications6. In particular, they have unique properties that make them attractive for studying the coherent properties of single-electron spins7,8,9,10,11. To perform such experiments it is necessary to confine a single electron in a quantum dot with highly tunable barriers1, but disorder has prevented tunable nanotube-based quantum-dot devices from reaching the single-electron regime2,3,4,5. Here, we use local gate voltages applied to an ultraclean suspended nanotube to confine a single electron in both a single quantum dot and, for the first time, in a tunable double quantum dot. This tunability is limited by a novel type of tunnelling that is analogous to the tunnelling in the Klein paradox of relativistic quantum mechanics.
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Acknowledgements
It is a pleasure to acknowledge P.L. McEuen for the suggestion of using p–n junctions as tunable barriers, as well as D. Loss, T. Balder, I.T. Vink, R.N. Schouten, L.M.K. Vandersypen, and M.H.M. van Weert for useful discussions and suggestions. This research was supported by the Dutch Organization for Fundamental Research on Matter (FOM), the Netherlands Organization for Scientific Research (NWO), and the Japan Science and Technology Agency International Cooperative Research Project (JST-ICORP).
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G.A.S. was responsible for the experimental work. All authors discussed the results and commented on the manuscript.
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Steele, G., Gotz, G. & Kouwenhoven, L. Tunable few-electron double quantum dots and Klein tunnelling in ultraclean carbon nanotubes. Nature Nanotech 4, 363–367 (2009). https://doi.org/10.1038/nnano.2009.71
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DOI: https://doi.org/10.1038/nnano.2009.71
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