@article{oai:ynu.repo.nii.ac.jp:00004171,
 author = {Sato, K. and Tahara, K. and Minami, Y. and Katayama, I. and Kawai, H. and Yanagi, K. and Takeda, J.},
 issue = {23},
 journal = {PHYSICAL REVIEW B},
 month = {Dec},
 note = {High-frequency coherent phonons resonantly excited inmetallic single-walled carbon nanotubes (M-SWCNTs)were investigated via spectrally resolved pump-probe spectroscopy using 7.5-fs laser pulses. In addition tofirst-order coherent phonons such as radial breathing mode (RBM) and M and G modes, we clearly observedsecond-order high-frequency coherent phonons of 2Dand 2Gmodes, which can be regarded as squeezed phonons.We found that the amplitudes of the RBM,Gand 2D modes were resonantly enhanced at specificwavelengths: themaximum resides at a wavelength whose energy is smaller than that of the van Hove singularities inM-SWCNTsby an amount corresponding to the phonon energy. Furthermore, the 2D mode has stronger enhancement than theother first-order Raman modes. These results indicate that the enhancement originates from a Stokes-stimulatedRaman-scattering process at van Hove singularities and that efficient resonance enhancement occurs for the 2Dmode, possibly through double resonance due to the trigonal warping effect and strong electron-phonon couplingdue to the Kohn anomaly.},
 title = {Resonance enhancement of first- and second-order coherent phonons in metallic single-walled carbon nanotubes},
 volume = {90},
 year = {2014}
}