Phonons in potassium doped graphene: the effects of electron-phonon interactions, dimensionality and ad-atom ordering
Physical Review B
American Physical Society
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 G-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 G-peak strongly softens and broadens. This is interpreted as a dynamic, non-adiabatic 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 remarkably similar for 1-4 layer graphene, but significantly different to doped bulk graphite.
We thank the EPSRC for funding, Felix Fernandez-Alonso, Andrew Walters, and Mark Ellerby for fruitful discussions, and Steve Firth for technical assistance. The work at Brookhaven is supported by the US DOE under Contract No. DEAC02- 98CH10886 and by the Center for Emergent Superconductivity, an Energy Frontier Research Center funded by the US DOE, Office of Basic Energy Sciences.
This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.
Vol. 84, 241404(R)