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Size and mobility of excitons in (6, 5) carbon nanotubes


Knowledge of excited-state dynamics in carbon nanotubes is determinant for their prospective use in optoelectronic applications. It is known that primary photoexcitations are quasi-one-dimensional excitons, the electron–hole correlation length (‘exciton size’) of which corresponds to a finite volume in the phase space. This volume can be directly measured by nonlinear spectroscopy provided the time resolution is short enough for probing before population relaxation. Here, we report on the experimental determination of exciton size and mobility in (6, 5) carbon nanotubes. The samples are sodium cholate suspensions of nanotubes (produced by the CoMoCat method) obtained by density-gradient ultracentrifugation. By using sub-15 fs near-infrared pulses to measure the nascent bleach of the lowest exciton resonance, we estimate the exciton size to be 2.0±0.7 nm. Exciton–exciton annihilation in our samples is found to be rather inefficient so that many excitons can coexist on a single nanotube.

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Figure 1: Two-dimensional pump–probe spectroscopy.
Figure 2: Pump intensity dependence of pump–probe kinetics.
Figure 3: Extraction of exciton size from the intensity-dependent bleach.

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This work was financially supported by the European Commission through the Human Potential Programme (Marie-Curie RTN BIMORE, Grant No. MRTN-CT-2006-035859) and by the National Science Foundation (NSF DMR-0606505). We acknowledge the financial support of the project FIRB SYNERGY.

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All authors contributed significantly to this work. In detail, project planning by G.L. and T.H., sample preparation and characterization by J.C. and T.H., measurement set-up and automation by D.P. and L.L., experiments by L.L. and S.H., data evaluation by L.L., G.L. and S.H., manuscript writing by L.L., G.L., T.H. and D.P.

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Correspondence to Larry Lüer.

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Lüer, L., Hoseinkhani, S., Polli, D. et al. Size and mobility of excitons in (6, 5) carbon nanotubes. Nature Phys 5, 54–58 (2009).

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