Ultrafast dynamics of the light-matter interaction in a charge-ordered molecular insulator α-(BEDT-TTF)2I3 were studied by pump-probe spectroscopy using few-optical-cycle infrared pulses (pulse width 12 fs). Coherent oscillation of the correlated electrons and subsequent Fano destructive interference with intramolecular vibration were observed in time domain; the results indicated a crucial role for electron-electron interplay in the light-matter interaction leading to the photoinduced insulator-to-metal transition. The qualitative features of this correlated electron motion were reproduced by calculations based on exact many-electron-phonon wave functions.
We report an optical modulation of the effective on-site Coulomb energy U on a dimer (U_{dimer}) for achieving the Mott insulator-to-metal transition in kappa-(BEDT-TTF)_{2}Cu[N(CN)_{2}]Br, as investigated by pump-probe spectroscopy. A reduction of U_{dimer} is optically induced by molecule displacement in the dimer under intradimer excitation. The mechanism of this metallization differs greatly from the photodoping-type mechanism reported previously. In contrast, a faster transition via the photodoping mechanism is detected for interdimer excitation. A metallic-domain-wall oscillation originating from the modulation of U_{dimer} was also observed near the critical end point of the Mott transition line.
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