The importance of inter-site coherences in the x-ray absorption spectra of mixed-valent systems

TL;DR

This paper highlights the critical role of inter-site coherences and quantum interference in accurately interpreting x-ray absorption spectra of mixed-valent systems, challenging conventional incoherent models.

Contribution

It introduces a multi-site approach that captures inter-site coherences and multiplet effects, improving the understanding of XAS in mixed-valent materials.

Findings

Conventional models fail to describe XAS in mixed-valent systems accurately.

Multi-site descriptions reveal forbidden multiplets in single-site approximations.

Inter-site coherences significantly influence XAS and RXS interpretations.

Abstract

We study the importance of inter-site coherences and quantum interference effects in the x-ray absorption spectroscopy (XAS) of mixed-valent systems. We demonstrate its importance, first for a simple diatomic mixed-valent molecule to elucidate the physics involved, and finally for mixed-valent Ti oxides, using a model calculation including full spin and orbital multiplicities. Our calculations demonstrate the inefficacy of conventional approaches of describing the XAS from mixed-valent systems as incoherent combinations of XAS from the pure-valent end members, and that multiplets forbidden in the single-site approximation can be reached within a multi-site description. These conclusions play an important role in the interpretation of XAS and resonant x-ray scattering (RXS) in terms of the electronic structure of strongly correlated systems.