Charge Transfer and dddd excitations in AgF2_{2}

Charge transfer (CT) insulators are the parent phase of a large group of today's unconventional high temperature superconductors. Here we study experimentally and theoretically the interband excitations of the CT insulator silver fluoride AgF$_2$, which has been proposed as an excellent analogue of oxocuprates. Optical conductivity and resonant inelastic x-ray scattering (RIXS) on AgF$_2$ polycrystalline sample show a close similarity with that measured on undoped La$_2$CuO$_4$. While the former shows a CT gap $\sim$3.4~eV, larger than in the cuprate, $dd$-excitations are nearly at the same energy in the two materials. DFT and exact diagonalization cluster computations of the multiplet spectra show that AgF$_2$ is more covalent than the cuprate, in spite of the larger fundamental gap. Furthermore, we show that AgF$_2$ is at the verge of a charge transfer instability. The overall resemblance of our data on AgF$_2$ to those published previously on La$_2$CuO$_4$ suggests that the underlying CT insulator physics is the same, while AgF$_2$ could also benefit from a proximity to a charge density wave phase as in BaBiO$_3$. Therefore, our work provides a compelling support to the future use of fluoroargentates for materials' engineering of novel high-temperature superconductors.Comment: 13 pages, 9 Figures (including SI

Open Data to "Charge-Transfer and dd excitations in AgF2"

AbstractData set corresponding to a published paper Journal: Phys. Rev. Research 4, 023108 (2022) DOI: 10.1103/PhysRevResearch.4.02310