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

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 ninth group of the periodic table to elucidate the emerging properties as d -orbitals change from partially filled 3 d to 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 the f -electron systems. Understanding the physics of transition metal oxides that move beyond the commonly studied 3 d orbital state is important for future studies. Taking the (CaCu 3 )B 4 O 12 family as an example, Meyers et al. examine the electronic and magnetic structure as the B-site changes from Co to Rh and Ir.