Competition between heavy-fermion and Kondo interaction in isoelectronic A-site ordered perovskites

TL;DR

This study investigates how electronic and magnetic properties evolve in A-site ordered perovskites with varying transition metals, revealing a transition from charge transfer states to heavy fermion behavior as d-orbitals change from 3d to 5d.

Contribution

It provides new insights into the competition between heavy-fermion and Kondo interactions in 4d and 5d transition metal oxides, extending understanding beyond traditional 3d systems.

Findings

Charge transfer from Zhang-Rice state to t2g orbital with decreasing d-electron count.

Observation of mixed-valence and heavy fermion states in specific compounds.

Mapping of these compounds onto the Doniach phase diagram for f-electron systems.

Abstract

With current research efforts shifting towards the 4$d$ and 5$d$ transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3$d$ materials is of critical importance. Here we perform X-ray spectroscopy and electronic structure calculations on $A$-site ordered perovskites with Cu in the $A$-site and the $B$-sites descending along the 9th group of the periodic table to elucidate the emerging properties as $d$-orbitals change from partially filled 3$d$, 4$d$, to 5$d$. The results show that when descending from Co to Ir the charge transfers from the cuprate like Zhang-Rice state on Cu to the t$_{2g}$ orbital of the B site. As the Cu $d$-orbital occupation approaches the Cu$^{2+}$ limit, a mixed-valence state in CaCu$_3$Rh$_4$O$_{12}$ and heavy fermion state in CaCu$_3$Ir$_4$O$_{12}$ are obtained. The investigated d-electron compounds are mapped onto the Doniach phase diagram of the competing RKKY and Kondo interactions developed for f-electron systems.