@article{oai:ynu.repo.nii.ac.jp:00004155,
 author = {Katayama, I and Sato, K and Takeda, J and Hishita, S and Fukidome, H and Suemitsu, M and Kitajima, M},
 issue = {24},
 journal = {Physical Review B},
 month = {Dec},
 note = {Coherent large-wave-vector phonons in graphene layers were excited by using a 7.5-fs ultrashort laser,and observed by wavelength-resolved pump-probe transient reflectivity spectroscopy. Inter-Dirac-cone electronscattering mediated by edges and defects in graphene layers drives large-wave-vector coherent D-mode phononsnear the Dirac point (K point) of the Brillouin zone. In contrast to the normal coherent phonons generated withfirst-order Raman process, phonon chirp is observed, and amplitude and frequency strongly change dependingon the probed wavelength. The results are discussed on the basis of doubly resonant Raman scattering process,demonstrating that generatedD-mode coherent phonons can propagate as nanoscale optical-phononwave packets.},
 title = {Coherent nanoscale optical-phonon wave packet in graphene layers},
 volume = {88},
 year = {2013}
}