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Photo-excited carrier dynamics, collinear scattering, and carrier multiplication in grapheme

9/01/2013, Marco Poloni, NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Pisa, Italy,

 

Graphene is emerging as a viable alternative to conventional optoelectronic, plasmonic, and nanophotonic materials. The interaction of light with graphene creates a non-equilibrium carrier distribution, which first relaxes on an ultrafast timescale to a hot Fermi-Dirac distribution and then cools via phonon emission. While the slower relaxation mechanisms have been extensively investigated, the very initial stages of relaxation, ruled by fundamental electron-electron (e-e) interactions, still pose a challenge. Experimentally, they defy the resolution of most pump-probe setups due to the extremely fast sub-100-fs carrier dynamics spanning a broad range of energies. Theoretically, the linear dispersion of massless Dirac fermions in graphene poses a novel many-body problem, fundamentally different from the parabolic-band model used for decades in ordinary metals and semiconductors. In this talk I will discuss recent results based on a pump-probe experiment featuring extreme temporal resolution (sub-10 fs) and broad spectral coverage. By comparing these results with a microscopic theory based on the semiclassical Boltzmann equation I will shed light on the fundamental physical mechanisms that control the non-equilibrium dynamics of hot carriers in graphene. I will discuss, in particular, the very significant role of collinear scattering, enabling Auger processes, including `carrier multiplication’, key to improving photovoltage generation and photodetectors.

Reference : D. Brida, A. Tomadin, C. Manzoni, Y.J. Kim, A. Lombardo, S. Milana, R.R. Nair, K.S. Novoselov, A.C. Ferrari, G. Cerullo, and M. Polini, arXiv:1209.5729 - under review.