Charge and structural dynamics in photoinduced phase transition of (EDO-TTF) ₂PF ₆ examined by picosecond time-resolved vibrational spectroscopy

Using time-resolved near-infrared reflectance spectroscopy and time-resolved mid-infrared vibrational spectroscopy, we studied photoinduced phase transition of the charge-ordered insulating phase in a charge-transfer complex (EDO-TTF) ₂PF ₆ (EDO-TTF: ethylenedioxy- tetrathiafulvalene) in the hundred picosecond range after photoexcitation. The temporal profiles at 0.83-1.03 eV, which are a characteristic of the photoinduced charge-disproportionate phase immediately after photoexcitation, suggested the formation of a new metastable phase in the hundred picosecond range. Time-resolved vibrational spectra at 1300-1700 cm ^-1, where charge- and structure-sensitive C=C stretching vibrational modes are located, elucidated that the nature of the new phase is very close to that of the high-temperature metallic phase and it takes about 100 ps for the new phase to emerge accompanied with charge and structure fluctuation.