Spin and orbital excitations in undoped infinite layers: a comparison between superconducting PrNiO2 and insulating CaCuO2

TL;DR

This study compares magnetic and orbital excitations in superconducting PrNiO2 and insulating CaCuO2 using RIXS, revealing similarities in spin and orbital properties despite differences in charge-transfer energy.

Contribution

It provides the first detailed comparison of spin and orbital excitations between nickelate and cuprate infinite-layer materials, highlighting shared properties.

Findings

PrNiO2 has smaller in-plane magnetic exchange than CaCuO2.

Orbital excitations are similar, except for the Ni-dxy peak which is lower in energy and has opposite dispersion.

Both materials support three-dimensional antiferromagnetic order.

Abstract

Infinite-layer nickelates are among the most promising cuprate-akin superconductors, although relevant differences from copper oxides have been reported. Here, we present momentum- and polarization-resolved RIXS measurements on chemically undoped, superconducting PrNiO2, and compare its magnetic and orbital excitations with those of the reference infinite layer cuprate CaCuO2. In PrNiO2, the in-plane magnetic exchange integrals are smaller than in CaCuO2, whereas the out-of-plane values are similar, indicating that both materials support a three-dimensional antiferromagnetic order. Orbital excitations, associated to the transitions within 3d states of the metal, are well reproduced within a single-ion model and display similar characteristics, except for the Ni-dxy peak which, besides lying at significantly lower energy, shows an opposite dispersion to that of Cu-dxy. This is interpreted as a consequence of orbital superexchange coupling between nearest neighbor sites, which drives the orbiton propagation. Our observations demonstrate that infinite layer cuprates and nickelates share most of the spin and orbital properties, despite their markedly different charge-transfer energy Delta.