Abstract
Photoexcitation is one of the promising methods to realize exotic states in materials. It possibly provides
us with ultrafast switching devices in the future. For research and development of such devices, it is
essential to understand the underlying physics in the ultrashort transient states induced by
photoexcitation. We have employed short-pulse x-ray free-electron laser to observe the dynamics of the
magnetic structure of the photoexcitated Mott insulator Sr2IrO4. We have performed time-resolved
resonant x-ray diffraction and time-resolved resonant x-ray inelastic scattering, and found that the nonequilibrium
state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but
hosts photo-carriers that retain strong, non-thermal magnetic correlations. These findings show that the
dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.
