Observation of excitonic effects in metallic single-walled carbon nanotubes

Abstract

Excitonic effects of metallic single-walled carbon nanotubes are measured with temperature-dependent resonant Raman spectroscopy. By changing the temperature in the range of 300--870 K, we observe variations in the optical transition energy ${E}_{ii}$ as well as in the maximum Raman intensity. We find both dependences to be different for semiconducting and metallic single-walled carbon nanotubes. We suggest an interpretation in terms of excitons dissociated into free electron-hole pairs at temperatures related to the exciton binding energy. We furthermore discuss how the oscillator strength is influenced by temperature.