Raman excitation profiles of metallic single-walled carbon nanotubes.

In this work Raman excitation profiles of metallic carbon nanotubes have been calculated and thoroughly analyzed. Suppression and vanishing of the high-energy resonance is completely confirmed by our calculations. The presented results clearly show that the suppression, and finally the absence, of the resonance is caused by electron-phonon interaction and interference effects. Electron-phonon coupling for low-energy resonance is significantly larger than for high-energy resonance. Furthermore, the transition energies of those two transitions are close enough to make interference effects important. The type of interference is determined by the sign of the electron-phonon interaction matrix elements. Constructive interference makes the low-energy resonance more intensive and destructive interference destroys the high-energy resonance for most of the metallic tubes.