Ultrafast Carrier Dynamics in Single-Wall Carbon Nanotubes

Time-resolved carrier dynamics in single-wall carbon nanotubes is investigated by means of two-color pump-probe experiments. The recombination dynamics is monitored by probing the transient photobleaching observed on the interband transitions of the semiconducting tubes. This dynamics takes place on a 1 ps time scale which is 1 order of magnitude slower than in graphite. Transient photoinduced absorption is observed for nonresonant probing and is interpreted as a global redshift of the $\pi$-plasmon resonance. We show that the opening of the band gap in semiconducting carbon nanotubes determines the nonlinear response dynamics over the whole visible and near-infrared spectrum.

Figure 1

Normalized change of transmission for a mixture of semiconducting and metallic SWCNTs in a degenerate pump/probe experiment at 0.8 eV (black line) and 1.47 eV (grey line). Inset: Linear optical absorption spectrum. $A$ and $B$ denote the peaks related to the semiconducting tubes, $C$ the one related to the metallic tubes, and $D$ the $\pi$-plasmon resonance.

Figure 2

Normalized change of transmission for a SWCNT’s mixture in two-color pump/probe experiments with a pump energy at 0.8 eV and a probe energy at 1.53 eV (black line) or 3.1 eV (grey line). The dashed line is a monoexponential fit with a time constant of 1 ps. Inset: Thin (thick) arrows on the OA spectrum indicate the probe (pump) energies; the black squares correspond to the relative amplitude of the signal when the pump is tuned near the top of the peak.

Figure 3

Normalized change of transmission for a pump (probe) energy of 0.8 eV (1.53 eV) calculated from the data obtained with a probe at 0.8 eV (black line), experimental signal (grey line).