Ultrafast dynamics of photoinduced semiconductor-to-metal transition in the optical switching nano-oxideTi3O5

Nanogranular trititanium pentaoxide $({\mathrm{Ti}}_{3}{\mathrm{O}}_{5})$, an oxide showing a photoreversible phase transition at room temperature, has recently attracted considerable attention because of its applicability in optical data storage. We report the dynamics of the photoinduced semiconductor-to-metal transition (\ensuremath{\beta} phase to \ensuremath{\lambda} phase) at room temperature. With time-resolved diffuse reflection spectroscopy conducted over a wide range of time scales, from femtoseconds to microseconds, the overall relaxation behavior was characterized. We found that a transient phase transition occurs within a few hundreds of femtoseconds and that 40% of the converted \ensuremath{\lambda}-phase fractions revert to \ensuremath{\beta} phase within 1 ps. Carriers are generated instantaneously and disappear within 20 ns. The \ensuremath{\lambda} phase increases from 1 to 10 ps, indicating growth of the metallic domain. A slow recovery process, with a duration ranging from ${10}^{\ensuremath{-}9}$ to ${10}^{\ensuremath{-}4}$ s, was found and is ascribed to the shrinking and annihilation of the size-distributed metastable \ensuremath{\lambda}-phase domains. The fast onset, with a duration within a few hundreds of femtoseconds and the subsequent stabilization process of less than 10 ps, signal the applicability of this material to ultrafast photoswitching.