Abstract
Graphene phonons are measured as a function of electron doping via the addition of potassium adatoms. In the low doping regime, the in-plane carbon peak hardens and narrows with increasing doping, analogous to the trend seen in graphene doped via the field effect. At high dopings, beyond those accessible by the field effect, the peak strongly softens and broadens. This is interpreted as a dynamic, nonadiabatic renormalization of the phonon self-energy. At dopings between the light and heavily doped regimes, we find a robust inhomogeneous phase where the potassium coverage is segregated into regions of high and low density. The phonon energies, linewidths, and tunability are notably very similar for one- to four-layer potassium-doped graphene, but significantly different to bulk potassium-doped graphite.
- Received 6 December 2010
DOI:https://doi.org/10.1103/PhysRevB.84.241404
©2011 American Physical Society