Coherent External and Internal Phonons in Quasi-One-Dimensional Organic Molecular Crystals
Abstract
We have directly time resolved coherent phonon oscillations in quasi-one-dimensional organic crystals of MePTCDI ( N-N'-dimethylperylene-3,4,9,10-dicarboximide), using femtosecond pump-probe experiments. We observe both higher-energy oscillations caused by intramolecular vibrations (internal phonons) and, for the first time in a quasi-one-dimensional organic system, lower-energy modulations which are related to coherent lattice phonons (external phonons). For internal Ag vibrations, the coherence decay time of about 2 ps is almost independent of the mode. In contrast, the damping time of the external phonons increases strongly with decreasing energy.
- Publication:
-
Physical Review Letters
- Pub Date:
- April 2001
- DOI:
- 10.1103/PhysRevLett.86.4060
- Bibcode:
- 2001PhRvL..86.4060H