Giant photoinduced lattice distortion in oxygen vacancy ordered SrCoO2.5 thin films

Despite the progress in understanding the formation and migration of oxygen vacancies in strongly correlated complex oxides, few studies focused on the dynamic behaviors of the oxygen vacancies under the transient and nonequilibrium states. Here we report a series of multitimescale ultrafast x-ray diffraction experiments using picosecond synchrotron and femtosecond table-top x-ray sources to monitor the structural dynamics in oxygen-vacancy-ordered $\mathrm{SrCo}{\mathrm{O}}_2.5$ thin films excited by photons. A giant photoinduced structure distortion in the $c$-axis direction (with strain $\mathrm{\ensuremath{\Delta}}c/c>1%$) was observed, higher than any previously reported data in the other transition metal oxide films. The femtosecond x-ray diffraction reveals the formation and propagation of the coherent acoustic phonons, indicating an instantaneous and a much larger photoinduced stress within the first 100 ps. Density functional theory reproduced the photostrictive responses and the strong dependence on excitation wavelength as observed in the experiments. The combined experimental and theoretic results demonstrate that the photoexcitation of the bonding to antibonding states via charge transfer is the dominant mechanism in the $\mathrm{SrCo}{\mathrm{O}}_2.5$ thin films, distinct from the depolarization effect by photoinduced carriers in the other perovskite oxides.