Observation of photo-induced insulator-to-metal transition in charge-ordered α-(BEDT-TTF)2I3 thin crystal by simultaneous transport and optical measurement

We accomplished simultaneous measurement of electrical conductance and optical transmittance changes induced by intramoleculer excitation using nanosecond pulse laser in a thin crystal of the organic conductor α-(BEDT-TTF)2I3 [BEDT-TTF=bis(ethylenedithio)tetrathiafulvalene] in the charge-ordered (CO) state aiming at observing the photo-induced state quantitatively. We evaluated both conductance and transmittance for the charge-transfer band in the photo-induced state. Experimental results suggest that a metastable CO melting phase grew over the entire area of the crystal. In addition, different conductance and transmittance behaviors were observed in terms of threshold and decay time, suggesting that the photo-induced phase grew inhomogeneously. ► We observed photo-induced insulator-to-metal transition in an α-(BEDT-TTF)2I3 thin crystal. ► We simultaneously evaluated conductance and transmittance in the photo-induced metallic state. ► The photo-induced metallic phase is charge order melting state caused by cooperative effect. ► The photo-induced metallic phase inhomogeneously grows.