Deciphering Femtosecond Charge-Lattice Dynamics in Textured LaFeO3 Thin Films.

Abstract

Understanding the intricate interplay between electronic and lattice dynamics is indispensable for controlling photoinduced functionality in correlated oxides. Here, we investigate the ultrafast relaxation pathways in textured LaFeO3 using femtosecond extreme-ultraviolet (XUV) absorption spectroscopy at the iron 3p edge. These nanosheets facilitate oriented perovskite growth on the amorphous Si3N4 membrane, giving rise to local epitaxy while preserving XUV transparency. By combining table-top time-resolved measurements with crystal-field multiplet calculations, we track the evolution from rapid ligand-to-metal charge transfer (LMCT) excitation to a lattice-stabilized polaronic state. The early-time response is dominated by the population of a mixed charge-transfer state with pronounced t2g3eg3 (5E) character, which indicates the initial electronic redistribution that follows photoexcitation. On subpicosecond time scales, the emergence of lattice-assisted carrier localization leads to partial charge localization and a lowering of the symmetry of Fe3+ sites. These changes suggest the formation of a polaronic state. At later delays, the transient spectra are governed by distorted Fe3+ configurations with residual charge-transfer character, without evidence for long-lived Fe2+ formation. Comparison with α-Fe2O3 reveals distinct material dependence in both charge-transfer relaxation and polaron-formation dynamics, demonstrating the roles of lattice topology and iron-oxygen covalency.