Abstract
Linear dispersion relations for the electron and hole energy spectra with zero energy band gap in graphene [1] provide nontrivial features like negative-dynamic conductivity in far infrared and terahertz (THz) spectral ranges [2]. Due to a very short time of the optical phonon emission τ0 ≈ 10−12s, the photogeneration of electrons and holes leads to the emission of a cascade of optical phonons, so that the photoelectrons and photoholes occupy the states with the energies close to εN = ħ(Ω/2-Nω0)< ħω0 , where ħΩ the pumping photon energy. ħω0 the optical phonon energy, and N the number of emitted optical phonons. As a consequence, photoelectrons/holes recombine to radiate THz photons with the energy ħω = 2 εN (inset in Fig. 1(a)) [1]. The incident photon spectra will reflect on the THz photoemission spectra as a proof of occurrence of such a process.
© 2009 IEEE
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