Charge density waves in infinite-layer NdNiO$_2$ nickelates

TL;DR

This study reports the discovery of charge density waves in infinite-layer NdNiO$_2$ films, revealing complex multi-orbital interactions and their disappearance upon superconductivity, thus advancing understanding of nickelate physics.

Contribution

It provides the first observation of charge density waves in infinite-layer nickelates and links them to orbital hybridisation, highlighting their role in the material's low-energy physics.

Findings

Charge density waves form at a specific wavevector in NdNiO$_2$.

CDWs involve Nd 5$d$ and Ni 3$d$ orbitals with out-of-plane dependence.

CDWs vanish when the material becomes superconducting at 20 ext% Sr doping.

Abstract

In materials science, much effort has been devoted to reproduce superconductivity in chemical compositions analogous to cuprate superconductors since their discovery over thirty years ago. This approach was recently successful in realising superconductivity in infinite-layer nickelates. Although differing from cuprates in electronic and magnetic properties, strong Coulomb interactions suggest infinite-layer nickelates have a propensity to various symmetry-breaking orders that populate the cuprates. Here we report the observation of charge density waves (CDWs) in infinite-layer NdNiO$_2$ films using Ni-$L_3$ resonant x-ray scattering. Remarkably, CDWs form in Nd 5$d$ and Ni 3$d$ orbitals at the same commensurate wavevector $(0.333, 0)\;r.l.u.$, with non-negligible out-of-plane dependence, and an in-plane correlation length up to $\sim$ 60 Angstrom. Spectroscopic studies reveal a strong connection between CDWs and the Nd 5$d$ - Ni 3$d$ orbital hybridisation. Upon entering the superconducting state at 20\% Sr doping, the CDWs disappear. Our work demonstrates the existence of CDWs in infinite-layer nickelates with a multi-orbital character distinct from cuprates, which establishes their low-energy physics.