Ultrafast Charge-Carrier Dynamics in Low-Dimensional Solids

Abstract

Ultrashort broadband THz pulses are applied to probe the femtosecond charge-carrier dynamics of laser-excited graphite and carbon nanotubes. In graphite, the electrons lose more than 90% of their excess energy which selectively heat up a very small subset of strongly coupled optical phonons. In the nanotube sample, the absence of a free-carrier response is due to the photogeneration of strongly bound excitons in the semiconducting tubes. A pronounced dichroism of a spectral feature of increased absorption gives direct evidence of excitations which are localized on a 100-nm length scale.