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Visualization and Manipulation of Bilayer Graphene Quantum Dots with Broken Rotational Symmetry and Nontrivial Topology

  • Zhehao Ge
    Zhehao Ge
    Department of Physics, University of California, Santa Cruz, California 95064, United States
    More by Zhehao Ge
  • Frederic Joucken
    Frederic Joucken
    Department of Physics, University of California, Santa Cruz, California 95064, United States
  • Eberth Quezada
    Eberth Quezada
    Department of Physics, University of California, Santa Cruz, California 95064, United States
  • Diego R. da Costa
    Diego R. da Costa
    Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, Campus do Pici, 60455-900 Fortaleza, Ceará, Brazil
  • John Davenport
    John Davenport
    Department of Physics, University of California, Santa Cruz, California 95064, United States
  • Brian Giraldo
    Brian Giraldo
    Jack Baskin School of Engineering, University of California, Santa Cruz, California 95064, United States
  • Takashi Taniguchi
    Takashi Taniguchi
    International Center for Materials Nanoarchitectronics, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
  • Kenji Watanabe
    Kenji Watanabe
    Research Center for Functional Materials, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
  • Nobuhiko P. Kobayashi
    Nobuhiko P. Kobayashi
    Jack Baskin School of Engineering, University of California, Santa Cruz, California 95064, United States
  • Tony Low
    Tony Low
    Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota 55455, United States
    More by Tony Low
  • , and 
  • Jairo Velasco Jr.*
    Jairo Velasco Jr.
    Department of Physics, University of California, Santa Cruz, California 95064, United States
    *Email: [email protected]
Cite this: Nano Lett. 2020, 20, 12, 8682–8688
Publication Date (Web):November 23, 2020
https://doi.org/10.1021/acs.nanolett.0c03453
Copyright © 2020 American Chemical Society

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    Abstract

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    Electrostatically defined quantum dots (QDs) in Bernal stacked bilayer graphene (BLG) are a promising quantum information platform because of their long spin decoherence times, high sample quality, and tunability. Importantly, the shape of QD states determines the electron energy spectrum, the interactions between electrons, and the coupling of electrons to their environment, all of which are relevant for quantum information processing. Despite its importance, the shape of BLG QD states remains experimentally unexamined. Here we report direct visualization of BLG QD states by using a scanning tunneling microscope. Strikingly, we find these states exhibit a robust broken rotational symmetry. By using a numerical tight-binding model, we determine that the observed broken rotational symmetry can be attributed to low energy anisotropic bands. We then compare confined holes and electrons and demonstrate the influence of BLG’s nontrivial band topology. Our study distinguishes BLG QDs from prior QD platforms with trivial band topology.

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    The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.nanolett.0c03453.

    • (1) Description of tip pulsing procedure, (2) sample fabrication, STM measurements, and tip cleaning, (3) circular symmetry of BLG QD, (4) reproducibility of BLG QD states, (5) numerical tight-binding calculations, (6) comparison between experimental dI/VS maps and simulated LDOS maps, (7) discussion on the importance of γ3, (8) evaluation of BLG QD state symmetry along different crystallographic directions, (9) BLG band structure with two different interlayer potential polarities, (10) heuristic for predicting orientation of real space LDOS distribution of BLG QD, (11) determination of the interlayer potential difference, (12) QD wave function orientation on top and bottom layers of BLG, (13) determination of upper and lower bounds for γ3 based on experiment and simulation comparison, (14) QD states probed with different gate and bias voltage combinations, (15) determination of QD lever arm; Figures S1–S19 showing STM and AFM images, schematic of hopping parameters, graphs, structures, band structures, and heuristic schematic (PDF)

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    Cited By

    This article is cited by 20 publications.

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