Model for a photoinduced insulator-metal transition in a one-dimensional quarter-filled organic salt: Evidence for a nonadiabatic charge-phonon coupling

We study the photoinduced nonequilibrium dynamics of a one-dimensional quarter-filled organic salt. Cooperative onsets of charge-order melting and coherent phonon generation are found in the early stage to τ∼ τex (where τex: the pulse length of the pumping laser), which signifies that they are mutually driven. Later, at τ□ τex, there is nonadiabatic decoupling of the charge-order melting and coherent phonon generation. Calculation of optical conductivity and time-resolved photoemission spectra at τ□ τex is consistent with the recent experimental observations, which confirms a nonadiabatic charge-phonon interaction in the ultrafast time span.