Raman excitation profile of the G band in single-chirality carbon nanotubes

We present in this work measurements of the Raman excitation profile of the high-energy phonons (G band) in single-chirality (n,m) semiconducting single-wall carbon nanotubes using more than 70 laser excitation energies, and a theoretical description based on the third-order quantum model for Raman scattering. We show that the observed asymmetry in the G band Raman excitation profile is rigorously explained by considering all physical elements associated with Raman scattering in (n,m) carbon nanotubes, such as the existence of van Hove singularities in the electronic density of states and wave-vector dependence of the matrix elements of the Raman process. We conclude that the proposed violation of the Condon approximation is not a fundamental principle underlying the nanotube photophysics.