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Evaluating covalency using resonant inelastic x-ray scattering spectral weights: Silver fluorides versus cuprates

Ilya Degtev1,2, Daniel Jezierski3, Adrián Gómez Pueyo1,2, Luciana Di Gaspare4, Monica De Seta4, Paolo Barone5, Giacomo Ghiringhelli6,7,*, Pieter Glatzel8, Zoran Mazej9 et al.

Wojciech Grochala3,†, Marco Moretti Sala6,‡, and José Lorenzana1,2,§

  • *Contact author: giacomo.ghiringhelli@polimi.it
  • †Contact author: w.grochala@cent.uw.edu.pl
  • ‡Contact author: marco.moretti@polimi.it
  • §Contact author: jose.lorenzana@cnr.it
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Phys. Rev. Research 8, 033094 – Published 23 July, 2026

DOI: https://doi.org/10.1103/qskv-2t7d

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 (CT) 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 measurement in the ligand K edge reveal a striking similarity between the fluoride and cuprate 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.

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Phys. Rev. Research 8, 033094– Published 23 July, 2026
  • Received 17 December 2025
  • Accepted 20 April 2026
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