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21 February 2011 Microscopic theory of ultrafast processes in carbon nanomaterials
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We evaluate a density matrix theory for the description of ultrafast relaxation processes in low-dimensional carbon nanostructures. The theory is based on Bloch equations describing the temporal dynamics of charge carrier population and transition probabilities. In combination with tight-binding wavefunctions, the approach allows the microscopic calculation of linear and nonlinear optical properties of graphene and carbon nanotubes with arbitrary chirality. This way, we have access to time- and momentum-resolved relaxation dynamics of non-equilibrium charge carriers. We study absorption spectra in graphene and carbon nanotubes illustrating the importance of excitonic effects in these structures including the formation of exciton-phonon induced side-bands in carbon nanotubes. Furthermore, we illustrate the relaxation of optically excited charge carriers toward equilibrium via electron-phonon and electron-electron scattering. We observe an ultrafast thermalization of excited carriers within the first hundred femtoseconds followed by a cooling of the electronic system on the picosecond time scale. Moreover, we investigate phonon-induced intersubband relaxation between the two energetically lowest transitions in nanotubes leading to a better understanding of photoluminescence excitation (PLE) experiments.
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Ermin Malic, Evgeny Bobkin, Torben Winzer, Christopher Köhler, Tobias Watermann, Matthias Hirtschulz, and Andreas Knorr "Microscopic theory of ultrafast processes in carbon nanomaterials", Proc. SPIE 7937, Ultrafast Phenomena in Semiconductors and Nanostructure Materials XV, 79371R (21 February 2011);

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