Electron Dynamics Probed by Time-Resolved Hard X-ray Photoelectron Spectroscopy

We have realized element-specific pump-probe time-resolved hard X-ray photoelectron spectroscopy (TR-HAXPES) for the study of ultrafast electron dynamics in condensed matter. TR-HAXPES has been applied for the first time to determine the temporal evolution of space-charge effects on Ti 1s core-level photoelectron spectra of SrTiO3 at the SACLA X-ray free electron laser facility. We found that the temporal evolution of Ti 1s kinetic energy shifts can be well explained by a mean-field model for the electron propagation in the vacuum. We also report preliminary results of a real-time laser-assisted valence-transition in YbInCu4, observed by measuring Yb 3d5/2 core-level HAXPES spectra at BL19LXU of SPring-8, under ON/OFF conditions of an optical pump-laser. We observed drastic changes in intensities of the Yb2+ and Yb3+ spectral components induced by pump-laser irradiation.