Theory of Anomalous X-ray Scattering in Orbital Ordered Manganites

TL;DR

This paper presents a theoretical study of anomalous X-ray scattering as a novel method to detect orbital orderings and excitations in perovskite manganites, emphasizing the role of Coulomb interactions and explaining experimental observations.

Contribution

It introduces a theoretical framework for anomalous X-ray scattering in manganites, highlighting the importance of Coulomb interactions for anisotropy and explaining forbidden reflections.

Findings

Orbital dependence of Coulomb interaction causes scattering anisotropy.

Calculated results explain observed forbidden reflections.

Discusses potential to observe orbital waves via X-ray scattering.

Abstract

We study theoretically the anomalous X-ray scattering as a new probe to observe the orbital orderings and excitations in perovskite manganites. The scattering matrix is given by the virtual electronic excitations from Mn $1s$ level to unoccupied Mn $4p$ level. We find that orbital dependence of the Coulomb interaction between Mn $3d$ and Mn $4p$ electrons is essential to bring about the anisotropy of the scattering factor near the K edge. The calculated results in $MnO_6$ clusters explain the forbidden reflections observed in $La_{0.5}Sr_{1.5}MnO_4$ and $LaMnO_3$. A possibility of the observation of the orbital waves by the X-ray scattering is discussed.