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

With current research efforts shifting towards the 4d and 5d transition metal oxides, understanding the evolution of the electronic and magnetic structure as one moves away from 3d materials is of critical importance. Here weX-ray spectroscopy and electronic structure calculations on A-site ordered perovskites with Cu in thesite and the B-sites descending along the 9th group of the periodic table to elucidate the emerging propertiesd-orbitals change from partially filled 3d, 4d, to 5d. The results show that when descending from Co to Ircharge transfers from the cuprate like Zhang-Rice state on Cu to the t2g orbital of the B site. As the Cuorbital occupation approaches the Cu2$+$ limit, a mixed-valence state in CaCu3Rh4O12 and heavy fermionin CaCu3Ir4O12 are obtained. The investigated d-electron compounds are mapped onto the Doniach phaseof the competing RKKY and Kondo interactions developed for f -electron systems.