Frequency splitting of intervalley phonons in graphene
Institut für Physik, Universität Augsburg - 86135 Augsburg, Germany, EU
2 Department of Physics, Bar-Ilan University - Ramat Gan 52900, Israel
Accepted: 18 June 2011
We study the thermal distribution of intervalley phonons in a graphene sheet. These phonons have two components with the same frequency. The degeneracy of the two modes is preserved by weak electron-phonon coupling. A sufficiently strong electron-phonon coupling, however, can result in a splitting into an optical and an acoustic phonon branch, which creates a fluctuating gap in the electronic spectrum. We describe these effects by treating the phonon distribution within a saddle-point approximation. Fluctuations around the saddle point indicate a Berezinskii-Kosterlitz-Thouless transition of the acoustic branch. This transition might be observable in the polarization of Raman scattered light.
PACS: 63.22.Rc – Phonons in graphene / 72.80.Vp – Electronic transport in graphene / 72.10.Di – Scattering by phonons, magnons, and other nonlocalized excitations
© EPLA, 2011