Ishioka, Kunie[National Institute for Materials Science > Advanced Nano-Characterization Center]
Hase, Muneaki[National Institute for Materials Science > Advanced Nano-Characterization Center]
Kitajima, Masahiro[National Institute for Materials Science > Advanced Nano-Characterization Center]
Wirtz, Ludger[CNRS UMR 8520 > Institute for Electronics, Microelectronics, and Nanotechnology]
Rubio, Angel[European Theoretical Spectroscopy Facility, Universidad del País Vasco, Centro Mixto CSIC-UPV/EHU and Donostia International Physics Center]
Petek, Hrvoje[Department of Physics and Astronomy, University of Pittsburgh and Donostia International Physics Center]
[en] We report the ultrafast dynamics of the 47.4 THz coherent phonons of graphite interacting with a photoinduced nonequilibrium 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 nonadiabatic electron-phonon interaction by creating a nonequilibrium electron-hole plasma. Time-resolved vibrational spectroscopy provides a window on the ultrafast nonquilibrium electron dynamics.