Mapping Dirac quasiparticles near a single Coulomb impurity on graphene
Abstract
The response of Dirac fermions to a Coulomb potential is predicted to differ significantly from how non-relativistic electrons behave in traditional atomic and impurity systems. Surprisingly, many key theoretical predictions for this ultra-relativistic regime have not been tested. Graphene, a two-dimensional material in which electrons behave like massless Dirac fermions, provides a unique opportunity to test such predictions. Graphene's response to a Coulomb potential also offers insight into important material characteristics, including graphene's intrinsic dielectric constant, which is the primary factor determining the strength of electron-electron interactions in graphene. Here we present a direct measurement of the nanoscale response of Dirac fermions to a single Coulomb potential placed on a gated graphene device. Scanning tunnelling microscopy was used to fabricate tunable charge impurities on graphene, and to image electronic screening around them for a Q=+1|e| charge state. Electron-like and hole-like Dirac fermions were observed to respond differently to a Coulomb potential. Comparing the observed electron-hole asymmetry to theoretical simulations has allowed us to test predictions for how Dirac fermions behave near a Coulomb potential, as well as extract graphene's intrinsic dielectric constant: ɛg=3.0+/-1.0. This small value of ɛg indicates that electron-electron interactions can contribute significantly to graphene properties.
- Publication:
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Nature Physics
- Pub Date:
- September 2012
- DOI:
- 10.1038/nphys2379
- arXiv:
- arXiv:1205.3206
- Bibcode:
- 2012NatPh...8..653W
- Keywords:
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- Condensed Matter - Mesoscale and Nanoscale Physics
- E-Print:
- Nat. Phys. 8, 653 (2012)