Shell Filling and Trigonal Warping in Graphene Quantum Dots

R. Garreis, A. Knothe, C. Tong, M. Eich, C. Gold, K. Watanabe, T. Taniguchi, V. Fal’ko, T. Ihn, K. Ensslin, and A. Kurzmann
Phys. Rev. Lett. 126, 147703 – Published 9 April 2021
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Abstract

Transport measurements through a few-electron circular quantum dot in bilayer graphene display bunching of the conductance resonances in groups of four, eight, and twelve. This is in accordance with the spin and valley degeneracies in bilayer graphene and an additional threefold “minivalley degeneracy” caused by trigonal warping. For small electron numbers, implying a small dot size and a small displacement field, a two-dimensional s shell and then a p shell are successively filled with four and eight electrons, respectively. For electron numbers larger than 12, as the dot size and the displacement field increase, the single-particle ground state evolves into a threefold degenerate minivalley ground state. A transition between these regimes is observed in our measurements and can be described by band-structure calculations. Measurements in the magnetic field confirm Hund’s second rule for spin filling of the quantum dot levels, emphasizing the importance of exchange interaction effects.

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  • Received 16 November 2020
  • Accepted 11 March 2021

DOI:https://doi.org/10.1103/PhysRevLett.126.147703

© 2021 American Physical Society

Physics Subject Headings (PhySH)

Quantum Information, Science & TechnologyCondensed Matter, Materials & Applied Physics

Authors & Affiliations

R. Garreis1,*, A. Knothe2, C. Tong1, M. Eich1, C. Gold1, K. Watanabe3, T. Taniguchi3, V. Fal’ko2,4, T. Ihn1, K. Ensslin1, and A. Kurzmann1

  • 1ETH Zurich (Swiss Federal Institute of Technology in Zurich), 8093 Zurich, Switzerland
  • 2National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom
  • 3National Institute for Material Science, 1-1 Namiki, Tsukuba 305-0044, Japan
  • 4Henry Royce Institute for Advanced Materials, M13 9PL, Manchester, United Kingdom

  • *garreisr@phys.ethz.ch

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Vol. 126, Iss. 14 — 9 April 2021

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