We report the ultrafast dynamics of the 47.4 THz coherent phonons of graphite interacting with a photoinduced non-equilibrium electron-hole plasma. Unlike conventional materials, upon photoexcitation the phonon frequency of graphite upshifts, and within a few picoseconds relaxes to the stationary value. Our first-principles density functional calculations demonstrate that the phonon stiffening stems from the light-induced decoupling of the non-adiabatic electron-phonon interaction by creating the non-equilibrium electron-hole plasma. Time-resolved vibrational spectroscopy provides a window on the ultrafast non-equilibrium electron dynamics.
@article{arxiv.0712.1879,
title = {Ultrafast Electron-Phonon Decoupling in Graphite},
author = {Kunie Ishioka and Muneaki Hase and Masahiro Kitajima and Ludger Wirtz and Angel Rubio and Hrvoje Petek},
journal= {arXiv preprint arXiv:0712.1879},
year = {2008}
}