Chirality dependence of coherent phonon amplitudes in single-wall carbon nanotubes

We simulate the ultrafast dynamics of laser-induced coherent phonons in single-wall carbon nanotubes (SWNTs). In particular, we examine the coherent phonon amplitude of the radial breathing mode (RBM) as a function of excitation energy and chirality. We find that the RBM coherent phonon amplitudes are very sensitive to changes in excitation energy and are strongly chirality dependent. We discuss how the SWNT diameter changes in response to femtosecond laser excitation and under what conditions the diameter of a given SWNT will initially increase or decrease. An effective-mass theory for the electron-phonon interaction gives a physical explanation for these phenomena.