Carrier dynamics in epitaxial graphene close to the Dirac point
  We study the carrier dynamics in epitaxially grown graphene in the range of photon energies from 10 - 250 meV. The experiments complemented by microscopic modeling reveal that the carrier relaxation is significantly slowed down as the photon energy is tuned to values below the optical phonon frequency, however, owing to the presence of hot carriers, optical phonon emission is still the predominant relaxation process. For photon energies about twice the value of the Fermi energy, a transition from pump-induced transmission to pump-induced absorption occurs due to the interplay of interband and intraband processes. 
Stephan Winnerl, Milan Orlita, Paulina Plochocka, Piotr Kossacki,   Marek Potemski, Torben Winzer, Ermin Malic, Andreas Knor...
cond-mat.mtrl-sci cond-mat.other