Disentangling charge and structural contributions during coherent atomic motions studied by ultrafast resonant x-ray diffraction

TL;DR

This study uses ultrafast resonant x-ray diffraction to distinguish between charge and structural dynamics in a manganite during photoinduced phase transition, revealing a coherent lattice mode that primarily modulates the structure.

Contribution

It introduces a method to separate charge and structural contributions in ultrafast x-ray diffraction, advancing understanding of phase transition mechanisms in complex oxides.

Findings

Identification of a 2.3 THz coherent structural mode

Charge order remains largely unaffected by the structural mode

Charge order drives the combined phase transition

Abstract

We report on the ultrafast dynamics of charge order and structural response during the photoinduced suppression of charge and orbital order in a mixed-valence manganite. Employing femtosecond time-resolved resonant x-ray diffraction below and at the Mn K absorption edge, we present a method to disentangle the transient charge order and structural dynamics in thin films of Pr0.5Ca0.5MnO3. Based on the static resonant scattering spectra, we extract the dispersion correction of charge ordered Mn3+ and Mn4+ ions, allowing us to separate the transient contributions of purely charge order from structural contributions to the scattering amplitude after optical excitation. Our finding of a coherent structural mode at around 2.3 THz, which primarily modulates the lattice, but does not strongly affect the charge order, confirms the picture of the charge order being the driving force of the combined charge, orbital and structural transition.