Visualization of photogenerated metallic inhomogeneity in the insulating   phase of Pr$_{\bf 0.7}$Ca$_{\bf 0.3}$MnO$_{\bf 3}$ thin film using   spatiotemporal terahertz radiation imaging
  Using a spatiotemporal terahertz radiation imaging technique, we visualize photogenerated metallic inhomogeneity in the charge-ordered insulating phase of Pr$_{0.7}$Ca$_{0.3}$MnO$_3$ thin film. We reveal that photogenerated metallic regions with micrometer length scales within the charge-ordered insulating matrix are created on subpicoseond time scales. Such an inhomogeneity becomes homogeneous when the laser power and bias voltage are increased. The observed photogenerated metallic regions would act as nucleus of the insulator-metal transition observed in Pr$_{0.7}$Ca$_{0.3}$MnO$_3$. 
N. Kida and M. Tonouchi
cond-mat.mtrl-sci