30 fs infrared spectroscopy of photo-induced phase transition in frac(1, 4) filling organic salt

Primary dynamics of photo-induced melting of charge order (CO) and metallic domain formation in [bis(ethlylenedithio)] tetrathiafulvalene (BEDT-TTF) salts α-(BEDT-TTF)₂I₃ were studied using an infrared (1.4 μm) pump-probe spectroscopy with a time resolution of 30 fs. Faster (<30 fs) and slower (ca. 2 ps) responses of transient reflectivity accompanying the coherent phonon were detected. They are attributable to the local melting of CO and the stabilization of semi-macroscopic metallic domain, respectively. Moreover, the correlation time (τ_cor) of the photo-induced insulator to metal transition was also measured by double-pulse excitation. The observed τ_cor (0.4 ps) is shorter than the stabilization time of the semi-macroscopic metallic domain.