Impact of Electron Correlations on Infinite-Layer Cuprates and Nickelates

TL;DR

This study compares the electron correlation strengths in infinite-layer PrNiO$_2$ and SrCuO$_2$ using advanced spectroscopic techniques, revealing that nickelates have unexpectedly stronger correlations than cuprates, which could influence superconductivity optimization.

Contribution

The paper provides a direct comparison of correlation strengths in nickelates and cuprates using combined XAS and RIXS, introducing a method to accurately determine the $U/t$ ratio in these materials.

Findings

PrNiO$_2$ has 20% stronger correlation strength than SrCuO$_2$.

Despite smaller Coulomb repulsion $U$, PrNiO$_2$ exhibits stronger correlations.

Moderating correlation strength could enhance superconductivity in nickelates.

Abstract

Optimization of unconventional superconductivity involves a balance of interaction strengths. Precise determination of correlation strength across different material families is therefore important. Here, we present a combined X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) study of infinite-layer PrNiO$_2$ and SrCuO$_2$ that enables fair comparison of their interaction strengths. For both compounds, we study the orbital and magnetic excitations and extract their dispersions along high-symmetry directions. Using a single-band Hubbard model and including higher-order exchange interactions, we derive the correlation factor $U/t$ for both compounds. A key finding is that despite a smaller Coulomb repulsion $U$, PrNiO$_2$ exhibits a correlation strength that is 20% stronger than that of its isostructural cuprate counterpart SrCuO$_2$. This indicates that a moderation of the correlation strength may further optimize superconductivity in nickelates.