Temperature-Dependent Ultrafast Response and π-Plasmon Dynamics in Single-Walled Carbon Nanotubes

Temperature-dependent femtosecond time-resolved carrier relaxation dynamics has been studied in thin films of single-walled carbon nanotubes. An early time evolution of the photoexcited relaxation shows evidence of superimposed transient bleaching and induced photo absorption of almost similar strengths, whereas at longer times it is governed by slow recovery of long-lived dark excitons. After about 3 ps, the signal is dictated by the slowest negative relaxation component attributed to the low-energy pi-plasmons. An absorption trough near 500 fs in the ultrafast response evolves with the increasing sample temperature. This particular feature is masked by the reduced induced transmission at room temperature and above. We have estimated the electron-phonon coupling constant to be similar to 0.86 from the linear temperature dependence of the slow relaxation time constant. More such studies can help advance the understanding of the intrinsic charge and energy loss mechanisms to improve the efficiency of the optoelectronic devices based on them.