Hidden correlations in stochastic photoinduced dynamics of a solid-state electrolyte

Photoexcitation by ultrashort laser pulses plays a crucial role in controlling reaction pathways and offering a microscopic view of complex dynamics at the molecular level. The photo response following a laser pulse is, in general, non-identical between multiple exposures due to spatiotemporal fluctuations in a material. However, most ultrafast experiments using a stroboscopic pump-probe scheme struggle to distinguish intrinsic sample fluctuations from extrinsic apparatus noise, often missing seemingly random deviations from the averaged shot-to-shot response. Leveraging the high photon-flux of time-resolved X-ray micro-diffraction at a synchrotron, we developed a method to characterize the shot-to-shot variation of the photoinduced dynamics in a solid-state electrolyte. By analyzing the evolution of the lattice parameter of a single grain in a powder ensemble, we found that there is a correlation between the nonequilibrium lattice trajectories following adjacent laser shots with a characteristic "correlation length" of approximately 1,500 shots, which represents an energy barrier of 0.38 eV for switching the photoinduced pathway, a value interestingly commensurate with the activation energy of lithium-ion diffusion. Not only does our method provide a new strategy for studying fluctuations in both condensed matter and molecular systems, it also paves the way for discovering hidden correlations and metastable states buried in oft-presumed random, uncorrelated fluctuating dynamics.