2009/02/27 by Yuanbo Zhang, Victor W. Brar, Çağlar Girit +3 · 8 citations
Materials Science · Physics and Astronomy · #Charge (physics) #Charge carrier #Condensed matter physics #Dirac (video compression format) #Dirac fermion #Electron #Fermion #Graphene #Graphene research and applications #Physics #Quantum Hall effect #Quantum and electron transport phenomena #Quantum mechanics #Scattering #Topological Materials and Phenomena #Wave function #cond-mat.mtrl-sci
paper · pdf · doi:10.1038/nphys1365
arxiv created 2009/02/27 · openalex publication_date 2009/08/30 · arxiv updated 2015/05/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
In an ideal graphene sheet charge carriers behave as two-dimensional (2D) Dirac fermions governed by the quantum mechanics of massless relativistic particles. This has been confirmed by the discovery of a half-integer quantum Hall effect in graphene flakes placed on a SiO2 substrate. The Dirac fermions in graphene, however, are subject to microscopic perturbations that include topographic corrugations and electron density inhomogeneities (i.e. charge puddles). Such perturbations profoundly alter Dirac fermion behavior, with implications for their fundamental physics as well as for future graphene device applications. Here we report a new technique of Dirac point mapping that we have used to determine the origin of charge inhomogeneities in graphene. We find that fluctuations in graphene charge density are not caused by topographical corrugations, but rather by charge-donating impurities below the graphene. These impurities induce unexpected standing wave patterns due to supposedly forbidden back-scattering of Dirac fermions. Such wave patterns can be continuously modulated by electric gating. Our observations provide new insight into impurity scattering of Dirac fermions and the microscopic mechanisms limiting electronic mobility in graphene.