Absence of $3a_0$ Charge Density Wave Order in the Infinite Layer Nickelates

TL;DR

This study shows that the previously reported charge density wave order in infinite layer nickelates is absent in pure NdNiO$_2$, indicating fundamental differences from cuprate superconductors and challenging previous interpretations.

Contribution

It provides evidence that charge density wave order is not present in NdNiO$_2$, clarifying the nature of electronic order in nickelates and refining the understanding of their phase diagram.

Findings

Charge density wave order is absent in NdNiO$_2$.

The observed superlattice peak is due to impurity phases.

Differences between nickelates and cuprates are highlighted.

Abstract

A hallmark of many unconventional superconductors is the presence of many-body interactions which give rise to broken symmetry states intertwined with superconductivity. Recent resonant soft x-ray scattering experiments report commensurate $3a_0$ charge density wave order in the infinite layer nickelates, which has important implications regarding the universal interplay between charge order and superconductivity in both the cuprates and nickelates. Here, we present x-ray scattering and spectroscopy measurements on a series of NdNiO$_{2+x}$ samples which reveal that the signatures of charge density wave order are absent in fully reduced, single-phase NdNiO$_2$. The $3a_0$ superlattice peak instead originates from a partially reduced impurity phase where excess apical oxygens form ordered rows with 3 unit cell periodicity. The absence of any observable charge density wave order in NdNiO$_2$ highlights a crucial difference between the phase diagrams of the cuprate and nickelate superconductors.