Time-resolved imaging and spectroscopy for the photo-induced phase transition in Ti4O7

• Time-resolved reflection imaging and spectroscopy were performed for Ti4O7.
• Ti4O7 shows insulator-metal phase transition at 140 K and 160 K.
• The growth of the metal domain could be observed through UV pulse irradiation.
• We derived the growth velocity from the dielectric functions as 1 × 104 m/s.
• The value is close to that of the acoustic phonon in the core titanium dioxide.

Time-resolved reflection imaging and spectroscopy were performed for single crystals of reduced-type titanium oxide Ti4O7. This shows two-step phase transition at 140 K from the low temperature (LT) phase to the intermediate (IT) phase and at 160 K from the IT phase to the high temperature (HT) phase. After the photo-irradiation in the IT phase, the time profiles of the reflection spectra and the excited area images showed spontaneous domain growth of the photo-induced HT phase. Analysis of the reflection images with the dielectric functions derived the growth velocity of the induced HT state. The value is close to that of the acoustic phonon in the core titanium dioxide.