Universal orbital and magnetic structures in infinite-layer nickelates

TL;DR

This study reveals universal orbital and magnetic structures in RNiO2 nickelates, showing similar magnetic excitations and hybridization, with charge order observed only in LaNiO2, highlighting fundamental electronic similarities and differences.

Contribution

It provides the first comparative analysis of orbital and magnetic structures across La, Pr, and Nd infinite-layer nickelates using RIXS, demonstrating their universality and identifying charge order variations.

Findings

Universal magnetic excitations confirmed in all three compounds.

Similar spin exchange coupling strengths across RNiO2.

Charge order observed only in LaNiO2.

Abstract

We conducted a comparative study of the rare-earth infinite-layer nickelates films, RNiO2 (R = La, Pr, and Nd) using resonant inelastic X-ray scattering (RIXS). We found that the gross features of the orbital configurations are essentially the same, with minor variations in the detailed hybridization. For low-energy excitations, we unambiguously confirm the presence of damped magnetic excitations in all three compounds. By fitting to a linear spin-wave theory, comparable spin exchange coupling strengths and damping coefficients are extracted, indicating a universal magnetic structure in the infinite-layer nickelates. Interestingly, while signatures of a charge order are observed in LaNiO2 in the quasi-elastic region of the RIXS spectrum, it is absent in NdNiO2 and PrNiO2. This prompts further investigation into the universality and the origins of charge order within the infinite-layer inickelates.