Ultrafast Light-Driven Electronic and Structural Changes in LaFeO₃ Perovskites Probed by Femtosecond X-Ray Absorption...

Area of Science:

• Materials Science
• Physical Chemistry
• Spectroscopy

Background:

• Real-time, element-specific studies of photo-excited systems are challenging.
• Femtosecond X-ray absorption spectroscopy (fs-XAS) using X-ray free-electron lasers (XFELs) offers a powerful solution.
• Understanding nonequilibrium dynamics in materials is crucial for advanced applications.

Purpose of the Study:

• To investigate light-driven ultrafast electronic and structural changes in epitaxial lanthanum iron oxide (LaFeO3) thin films.
• To elucidate the mechanisms behind these dynamic transformations using advanced spectroscopic techniques.
• To correlate experimental observations with theoretical calculations for a comprehensive understanding.

Main Methods:

• Femtosecond X-ray absorption spectroscopy (fs-XAS) performed at the PAL-XFEL.
• Density functional theory (DFT) calculations.
• Multiplet calculations to interpret spectroscopic data.

Main Results:

• Photoexcitation induces high- and intermediate-spin Fe2+ states via ligand-to-metal charge transfer (LMCT).
• Subsequent polaron formation was observed.
• Reduced overlap between oxygen 2p and iron 3d orbitals explains all experimental findings, including XAS energy shifts and crystal field splitting changes.

Conclusions:

• Fs-XAS successfully unravels ultrafast electronic and structural dynamics in LaFeO3 thin films.
• The study demonstrates the critical role of reduced orbital overlap in governing photoinduced changes.
• This work provides fundamental insights into the behavior of photo-excited oxide materials.