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Open Access Publications from the University of California

Imaging electrostatically confined Dirac fermions in graphene quantum dots

  • Author(s): Lee, Juwon
  • Wong, Dillon
  • Velasco Jr, Jairo
  • Rodriguez-Nieva, Joaquin F
  • Kahn, Salman
  • Tsai, Hsin-Zon
  • Taniguchi, Takashi
  • Watanabe, Kenji
  • Zettl, Alex
  • Wang, Feng
  • Levitov, Leonid S
  • Crommie, Michael F
  • et al.

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© 2016 Macmillan Publishers Limited. All rights reserved. Electrostatic confinement of charge carriers in graphene is governed by Klein tunnelling, a relativistic quantum process in which particle-hole transmutation leads to unusual anisotropic transmission at p-n junction boundaries. Reflection and transmission at these boundaries affect the quantum interference of electronic waves, enabling the formation of novel quasi-bound states. Here we report the use of scanning tunnelling microscopy to map the electronic structure of Dirac fermions confined in quantum dots defined by circular graphene p-n junctions. The quantum dots were fabricated using a technique involving local manipulation of defect charge within the insulating substrate beneath a graphene monolayer. Inside such graphene quantum dots we observe resonances due to quasi-bound states and directly visualize the quantum interference patterns arising from these states. Outside the quantum dots Dirac fermions exhibit Friedel oscillation-like behaviour. Bolstered by a theoretical model describing relativistic particles in a harmonic oscillator potential, our findings yield insights into the spatial behaviour of electrostatically confined Dirac fermions.

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