Observation of correlated plasmons in low-valence nickelates

TL;DR

This study reports the first observation of plasmons in low-valence nickelates using RIXS, revealing unique charge dynamics and screening effects that differ from cuprates, advancing understanding of correlated electron behavior in nickelate superconductors.

Contribution

First experimental detection of plasmons in nickelates, providing insights into their charge dynamics and screening, and comparing them to cuprate superconductors.

Findings

Nickelate plasmons are more damped and slower than in cuprates.

Plasmons soften with increasing temperature in nickelates.

Charge screening landscape in nickelates differs from cuprates.

Abstract

The discovery of nickelate superconductors has opened a new arena for studying the behavior of correlated electron liquids that give rise to unconventional superconductivity. While critical information about a material's charge dynamics is encoded in its plasmons, collective modes of the electron gas, these excitations have not yet been observed in nickelate materials. Here, we use resonant inelastic x-ray scattering (RIXS) to detect plasmons in the metallic, low-valence nickelate Pr4Ni3O8. Although qualitatively similar to those in cuprates, the nickelate plasmons are more heavily damped and have a lower velocity than those in a cuprate at comparable doping, which we attribute to reduced electronic hopping and enhanced screening of the long-range Coulomb interactions. Furthermore, the plasmons in Pr4Ni3O8 soften with increasing temperature, in contrast to the cuprate, where plasmons remain at nearly fixed energy but become more strongly damped. Taken together, these results reveal a distinct charge-screening landscape in nickelates and place quantitative constraints on analogies to cuprates.