Strength of Correlations in a Silver Based Cuprate Analogue

TL;DR

This study investigates the electronic correlations in AgF2, confirming it as a charge-transfer insulator similar to cuprates, and discusses its potential as a high-temperature superconductor upon doping, using spectroscopy and computational methods.

Contribution

It provides the first detailed spectroscopic and computational analysis of AgF2's electronic correlations, classifying it as a cuprate analogue based on the Zaanen-Sawatzky-Allen scheme.

Findings

AgF2 is a charge-transfer correlated insulator.

AgF2 shares electronic correlation characteristics with cuprates.

Doping could potentially induce high-temperature superconductivity.

Abstract

AgF2 has been proposed as a cuprate analogue which requires strong correlation and marked covalence. On the other hand, fluorides are usually quite ionic and 4d transition metals tend to be less correlated than their 3d counterparts, which calls for further scrutiny. We combine valence band photoemission and Auger-Meitner spectroscopy of AgF and AgF2 together with computations in small clusters to estimate values of the Ag 4d Coulomb interaction U 4d and charge-transfer energy. Based on these values, AgF2 can be classified as a charge-transfer correlated insulator according to the Zaanen-Sawatzky-Allen classification scheme. Thus, we confirm that the material is a cuprate analogue from the point of view of correlations, suggesting that it should become a high-temperature superconductor if metallization is achieved by doping. We present also a computation of the Hubbard U in density functional "+U" methods and discuss its relation to the Hubbard U in spectroscopies.