Hot Dirac Fermions in Epitaxial Graphene
  We investigate the ultrafast relaxation dynamics of hot Dirac fermionic quasiparticles in multilayer epitaxial graphene using ultrafast optical differential transmission spectroscopy. We observe DT spectra which are well described by interband transitions with no electron-hole interaction. Following the initial thermalization and emission of high-energy phonons, the electron cooling is determined by electron-acoustic phonon scattering, found to occur on the time scale of 1 ps for highly doped layers, and 4-11 ps in undoped layers. The spectra also provide strong evidence for the multilayer stucture and doping profile of thermally grown epitaxial graphene on SiC. 
Dong Sun, Zong-Kwei Wu, Charles Divin, Xuebin Li, Claire Berger, Walt   A. de Heer, Phillip N. First, and Theodore B. Norris