The photo-induced phase and coherent phonon in the organic conductor (EDO-TTF)₂PF₆

We have investigated the nature of the photo-induced state and coherent phonon in the conducting charge transfer complex (EDO-TTF)₂PF ₆ by measuring the ultrafast reflectivity change over a wide photon energy range from 0.069 eV (18 ν m) to 2.1 eV (580 nm). The photo-induced spectra just after photo-excitation indicate that the photo-induced phase is similar to but clearly different from that in a thermally induced metal phase though they are the same for general photo-induced phase transition. The temporal profiles at each probe photon energy are accompanied by extraordinarily large amplitude oscillation originating from coherent phonon generation. The period of the coherent phonon depends discretely on the probe photon energy, while the generation efficiency of both the photo-induced phase and coherent photon reaches a maximum when the peak top of a charge transfer band is excited. These results are probably attributable to the strong electron-vibration coupling in this complex.