Ultrafast structural dynamics of the Fe-pnictide parent compound BaFe2As2

TL;DR

This study uses femtosecond x-ray diffraction to explore ultrafast structural changes in BaFe2As2, revealing how coherent phonon excitation affects the Fe-As tetrahedra and influences magnetic moments, with implications for electron-phonon interactions.

Contribution

It provides the first quantification of coherent structural dynamics and electron-phonon coupling in BaFe2As2 using time-resolved x-ray diffraction and photoemission data.

Findings

Observation of fluence-dependent Bragg oscillations

Quantification of Fe-As tetrahedra modifications

Determination of electron-phonon deformation potential

Abstract

Using femtosecond time-resolved x-ray diffraction we investigate the structural dynamics of the coherently excited A1g phonon mode in the Fe-pnictide parent compound BaFe2As2. The fluence dependent intensity oscillations of two specific Bragg reflections with distinctly different sensitivity to the pnictogen height in the compound allow us to quantify the coherent modifications of the Fe-As tetrahedra, indicating a transient increase of the Fe magnetic moments. By a comparison with time-resolved photoemission data we derive the electron-phonon deformation potential for this particular mode. The value of Delta mu/Delta z = -(1.0 - 1.5) eV/A is comparable with theoretical predictions and demonstrates the importance of this degree of freedom for the electron-phonon coupling in the Fe pnictides.