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

Abstract

We have investigated the nature of the photo-induced state and coherent phonon in the conducting charge transfer complex (EDO-TTF) 2 PF 6 by measuring the ultrafast reflectivity change over a wide photon energy range from 0.069 eV (18 μm) 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.

Charge and Structural Dynamics in Photoinduced Phase Transition of (EDO-TTF)2PF6 Examined by Picosecond Time-Resolved Vibrational Spectroscopy

“…According to a previous report, the dynamical change in the spectral shape in the vis–IR region indicated that the lifetime of the (1010) charge-disproportionate phase is within 5 ps . The present results shown in Figure are closely consistent with this result.…”

“…According to a previous report, the dynamical change in the spectral shape in the vis−IR region indicated that the lifetime of The Journal of Physical Chemistry C the (1010) charge-disproportionate phase is within 5 ps. 36 The present results shown in Figure 4 are closely consistent with this result. Therefore, we conclude that the fast decay process commonly observed at 1424 and 1572 cm −1 is due to electronic relaxation of the photoinduced (1010) phase.…”

“…The excitation density was 2.0 mJ/cm 2 (8.0 × 10 15 photons/cm 2 ). In a previous report, the direction of the reflectivity change in this probe photon energy region was a key to assign the photoinduced phase. That is, a positive reflectivity change indicates the appearance of a phase similar to the thermally induced metallic phase, whereas a negative reflectivity change indicates the generation of the photoinduced (1010) charge-disproportionate phase.…”

Off-Planar Geometry and Structural Instability of EDO-TTF Explained by Using the Extended Debye Polarizability Model for Bond Angles

“…It is estimated that only one in 500–1500 molecules , is excited by such a pulse. How such a local event leads to a bulk phase transition is subject of speculation. ,− One possibility we see is the scenario in which a neutral bent molecule is excited to become planar. The geometry change could affect a neighbor molecule to also change geometry, thereby propagating the effect of the excitation.…”

Local response to light excitation in the charge-ordered phase of(EDO−TTF)2SbF6

“…Such ultrafast oscillation of optical reflectivity is generated by the activation of coherent optical phonons, which modulate the dielectric susceptibility through electron-phonon coupling. The contribution of a specific phonon to optical modulation is photon energy dependent [33] and explains the apparent relative change of the spectral weight of the modes for measurements using 0.83 and 1.72 eV probes.…”