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arXiv · 1212.3993

Dielectric screening of the Kohn anomaly of graphene on hexagonal boron nitride

F. Forster·A. Molina-Sanchez·S. Engels·A. Epping·K. Watanabe·T. Taniguchi·L. Wirtz·C. Stampfer
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Abstract

Kohn anomalies in three-dimensional metallic crystals are dips in the phonon dispersion that are caused by abrupt changes in the screening of the ion-cores by the surrounding electron-gas. These anomalies are also present at the high-symmetry points Γand K in the phonon dispersion of two-dimensional graphene, where the phonon wave-vector connects two points on the Fermi surface. The linear slope around the kinks in the highest optical branch is proportional to the electron-phonon coupling. Here, we present a combined theoretical and experimental study of the influence of the dielectric substrate on the vibrational properties of graphene. We show that screening by the dielectric substrate reduces the electron-phonon coupling at the high-symmetry point K and leads to an up-shift of the Raman 2D-line. This results in the observation of a Kohn anomaly that can be tuned by screening. The exact position of the 2D-line can thus be taken also as a signature for changes in the (electron-phonon limited) conductivity of graphene.

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F. Forster, A. Molina-Sanchez, S. Engels, A. Epping, K. Watanabe, T. Taniguchi, L. Wirtz, C. Stampfer. 2013-08-12. Dielectric screening of the Kohn anomaly of graphene on hexagonal boron nitride. https://doi.org/10.1103/physrevb.88.085419

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