Charged-impurity scattering in graphene

Charged-impurity scattering in graphene
J. H. Chen장차운S. AdamM. S. FuhrerE. D. WilliamsM. Ishigami
Issue Date
Nature physics
VOL 4, NO 5, 377-381
Since the initial demonstration of the ability to experimentally isolate a single graphene sheet1, a great deal of theoretical work has focused on explaining graphene’s unusual carrierdensity- dependent conductivity σ(n), and its minimum value (σmin) of nearly twice the quantum unit of conductance (4e2/ h) (refs 1–6). Potential explanations for such behaviour include short-range disorder7–10, ‘ripples’ in graphene’s atomic structure11,12 and the presence of charged impurities7,8,13–18. Here, we conduct a systematic study of the last of these mechanisms, by monitoring changes in electronic characteristics of initially clean graphene19 as the density of charged impurities (nimp) is increased by depositing potassium atoms onto its surface in ultrahigh vacuum. At non-zero carrier density, charged-impurity scattering produces the widely observed linear dependence1–6 of σ(n).More significantly,we find that min occurs not at the carrier density that neutralizes nimp, but rather the carrier density at which the average impurity potential is zero15. As nimp increases, σmin initially falls to a minimum value near 4e2/ h. This indicates that σmin in the present experimental samples1–6 is governed not by the physics of the Dirac point singularity20,21, but rather by carrier-density inhomogeneities induced by the potential of charged impurities6,8,14,15.
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