Electron-Phonon Coupling Of G Mode And Assignment Of A Combination Mode In Carbon Nanotubes

We measure the electron-phonon (e-ph) coupling matrix elements of the G band in semiconducting carbon nanotubes (CNTs) in comparison to the radial breathing mode (RBM). The experimental result for the G(+) mode [Gamma-point longitudinal optical (LO) phonon] at the E-22 transition suggests an e-ph coupling strength of approximately 30 meV or 12.5 eV/angstrom, which is within the expected range of 23 meV to 83 meV for a 1-nm-diameter CNT. This coupling (as the square of the matrix elements) for the G(+) mode is an order of magnitude higher than that of the RBM and other measured phonon modes. In addition we assign a Raman feature observed around 1700 cm(-1) to be the combination mode of a low energy (similar to 400 cm(-1)) and a high energy (similar to 1300 cm(-1)) zone-boundary phonon. Both the phonon energies and phonon dispersions of those modes support the assignment.