Magnetic exchange coupling in cuprate-analog $d^9$ nickelates

TL;DR

This study investigates the magnetic exchange interaction in layered $d^9$ nickelates, revealing that certain nickelates have a large exchange interaction similar to high-$T_c$ cuprates, which is significant for understanding their superconducting potential.

Contribution

The paper demonstrates that engineered layered $d^9$ nickelates can have a large magnetic exchange interaction comparable to cuprates, providing insight into their similarities and potential for high-temperature superconductivity.

Findings

Nickelates studied have $J$ around 100 meV.

Certain nickelates are free from self-doping effects.

Nickelates share magnetic properties with high-$T_c$ cuprates.

Abstract

Motivated by the recent discovery of superconductivity in doped NdNiO$_2$, we study the magnetic exchange interaction $J$ in layered $d^9$ nickelates from first principles. The mother compounds of the high-$T_{\rm c}$ cuprates belong to the charge-transfer regime in the Zaanen-Sawatzky-Allen diagram and have $J$ larger than 100 meV. While this feature makes the cuprates very different from other transition metal oxides, it is of great interest whether layered $d^9$ nickelates can also have such a large $J$. However, one complexity is that NdNiO$_2$ is not a Mott insulator due to carrier doping from the block layer. To compare the cuprates and $d^9$ nickelates on an equal basis, we study RbCa$_2$NiO$_3$ and $A_{2}$NiO$_{2}$Br$_2$ ($A$: a cation with the valence of $2.5+$), which were recently designed theoretically by block-layer engineering. These nickelates are free from the self-doping effect and belong to the Mott-Hubbard regime. We show that these nickelates share a common thread with the high-$T_{\rm c}$ cuprates in that they also have a significant exchange interaction $J$ as large as about 100 meV.