Evaluating covalency using RIXS spectral weights: Silver fluorides vs. cuprates

TL;DR

This study uses RIXS spectral weights to evaluate covalency in silver fluorides compared to cuprates, revealing similarities that suggest silver fluorides as promising models for high-temperature superconductivity research.

Contribution

It introduces a novel method using RIXS spectral weight ratios to quantify covalency and compares fluorides with cuprates, highlighting their potential for superconductivity studies.

Findings

AgF2 shows charge transfer and dd excitations similar to La2CuO4.

Fluorides are more covalent than cuprates based on spectral weight analysis.

Silver fluorides are promising platforms to mimic cuprate physics.

Abstract

We investigate the electronic structure of AgF2, AgFBF4, AgF and Ag2O using X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) at the Ag L3 edge. XAS results were compared with density functional theory computations of the spectra, allowing an identification of main features and an assessment of the theoretical approximations. Our RIXS measurements reveal that AgF2 exhibits charge transfer excitations and dd excitations, analogous to those observed in La2CuO4. We propose to use the ratio of dd to CT spectral weight as a measure of the covalence of the compounds and provide explicit equations for the weights as a function of the scattering geometry for crystals and powders. The measurements at the metal site L3 edge and previous measurements at the ligand K edge reveal a striking similarity between the fluorides and cuprates materials, with fluorides somewhat more covalent than cuprates. These findings support the hypothesis that silver fluorides are an excellent platform to mimic the physics of cuprates, providing a promising avenue for exploring high-Tc superconductivity and exotic magnetism in quasi-two-dimensional (AgF2) and quasi-one-dimensional (AgFBF4) materials.