Dresden 2006 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 9: Poster I

HL 9.71: Poster

Montag, 27. März 2006, 15:15–17:45, P3

Charge carrier dynamics in graphite and carbon nanotubes observed by time-resolved THz spectroscopy — •Tobias Kampfrath, Luca Perfetti, Christian Frischkorn, and Martin Wolf — Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin

Ultrafast charge carrier dynamics in graphite and carbon nanotubes have been investigated by time-resolved THz spectroscopy. In graphite, analysis of the transient dielectric function between 10 and 30 THz and model calculations show that more than 90 % of the initially deposited excitation energy is transferred to few strongly coupled lattice vibrations within 500 fs. These hot optical phonons also substantially contribute to the striking increase of the Drude relaxation rate observed during the first ps after photoexcitation. The subsequent cooling of the hot phonons yields a lifetime estimate of 7 ps for these modes [1].

The response of the nantoube sample lacks a distinct free-carrier response which is attributed to the photogeneration of strongly bound excitons in the tubes with large energy gaps. We find a feature of enhanced transmission caused by the blocking of optical transitions in small-gap tubes. The rapid decay of a featureless background with pronounced dichroism is associated with the increased hopping rate of spatially localized charge carriers before thermalization is completed.

[1] Phys. Rev. Lett. 95, 187403 (2005)