Ultrafast light-driven electronic and structural changes in LaFeO3 perovskites probed by femtosecond X-ray absorption spectroscopy

This repository contains the data used in Figures 2 and 3 of the manuscript titled "Ultrafast light-driven electronic and structural changes in LaFeO3 perovskites probed by femtosecond X-ray absorption spectroscopy", Advanced Materials, 2025 (https://doi.org/10.1002/adma.202502932).
Abstract: Conducting real-time, element-specific studies of photoexcited systems has been a long-standing challenge. The development of X-ray free-electron lasers (XFELs) has paved the way for the emergence of a promising technique: femtosecond X-ray absorption spectroscopy (fs-XAS). This powerful technique reveals electronic and geometric characteristics, providing unprecedented insight into their dynamic interactions under non-equilibrium conditions. Herein, we employ the fs-XAS technique at PAL-XFEL to unravel light-driven ultrafast electronic and structural changes in epitaxial lanthanum iron oxide (LaFeO3) thin films. We have utilized density functional theory (DFT) and multiplet calculations to expound on the experimental results. Our analyses reveal that photoexcitation initially induces high- and intermediate-spin Fe2+ states through ligand-to-metal charge transfer (LMCT), followed by polaron formation. We demonstrate that the reduced overlap between the oxygen 2p and iron 3d orbitals accounts for all experimental observations, including (1) the XAS shifts to lower energies, (2) the decrease in the crystal field splitting, and (3) the relatively larger shifts observed in the oxygen 1s XAS.