Mechanism of the far-infrared absorption of carbon-nanotube films.
The far-infrared conductivity of single-wall carbon-nanotube ensembles is dominated by a broad absorption peak around 4 THz whose origin is still debated. We observe an overall depletion of this peak when the nanotubes are excited by a short visible laser pulse. This finding excludes optical absorption due to a particle-plasmon resonance and instead shows that interband transitions in tubes with an energy gap of approximately 10 meV dominate the far-infrared conductivity. A simple model based on an ensemble of two-level systems naturally explains the weak temperature dependence of the far-infrared conductivity by the tube-to-tube variation of the chemical potential.
Fachbereich Physik, Freie Universität Berlin, 14195 Berlin, Germany.
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T
Kampfrath
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K
von Volkmann
C M
CM
Aguirre
P
P
Desjardins
R
R
Martel
M
M
Krenz
C
C
Frischkorn
M
M
Wolf
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Perfetti