Strong phonon-plasmon coupled modes in the graphene/silicon carbide heterosystem

Abstract

We report on strong coupling of the charge carrier plasmon ${\omega }_{PL}$ in graphene with the surface optical phonon ${\omega }_{SO}$ of the underlying SiC(0001) substrate with low electron concentration ($n=1.2\times 10^{15}$ $c{m}^{-3}$) in the long wavelength limit ($q_{\parallel }\to 0$). Energy dependent energy-loss spectra give for the first time clear evidence of two coupled phonon-plasmon modes ${\omega }_{\pm }$ separated by a gap between ${\omega }_{SO}$ ($q_{\parallel }\to 0$) and ${\omega }_{TO}$ ($q_{\parallel }>>0$), the transverse optical phonon mode, with a Fano-type shape, in particular for higher primary electron energies ($E_0\ge 20eV$). A simplified model based on dielectric theory is able to simulate our energy - loss spectra as well as the dispersion of the two coupled phonon-plasmon modes ${\omega }_{\pm }$. In contrast, Liu and Willis [1] postulate in their recent publication no gap and a discontinuous dispersion curve with a one-peak structure from their energy-loss data.

4 pages, 3 figures, presented during Graphene Week 2010, Maryland University, College Park, Maryland, USA, April 19-23, 2010

References in corpus (5)

• The electronic properties of graphene
• Ultrathin epitaxial graphite: 2D electron gas properties and a route toward graphene-based nanoelectronics
• Substrate limited electron dynamics in graphene
• Collective modes of the massless Dirac plasma
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