Raman excitation profile of theGband in single-chirality carbon nanotubes

Abstract

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.