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Observation of Correlated Plasmons in Low-Valence Nickelates

Y. Shen1,*,§, W. He1,2, J. Sears1, Xuefei Guo1, Xiangpeng Luo1, A. Roll1, J. Li3, J. Pelliciari3, Xi He1 et al.

I. Božovič1,4,†, Junjie Zhang5,6, J. F. Mitchell5, V. Bisogni3, M. Mitrano7, S. Johnston8,9, and M. P. M. Dean1,8,‡

  • *Contact author: yshen@iphy.ac.cn
  • †Present address: Shanghai Advanced Research in Physical Sciences (SHARPS), Pudong, Shanghai 201203, China.
  • ‡Contact author: mdean@bnl.gov
  • §Present address: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
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Phys. Rev. X 16, 031031 – Published 7 August, 2026

DOI: https://doi.org/10.1103/3ycq-jclr

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 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.

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Popular Summary

The collective modes of an electron gas, called plasmons, are an essential window into electronic interactions in metals and their role in low-temperature instabilities such as superconductivity. In recent years, significant progress has been made in measuring plasmon excitations in cuprate superconductors, while corresponding measurements in nickelate superconductors remain lacking. Here, we report the direct observation of plasmons in the low-valence nickelate Pr4Ni3O8. Our measurements reveal that nickelate plasmons resemble those in copper oxide superconductors, but propagate more slowly, decay faster, and uniquely soften as temperature rises. These findings indicate that charge dynamics in nickelates involve stronger electronic compressibility and altered screening of electric forces compared with their cuprate counterparts. Our study establishes firm experimental constraints on theoretical models of the electronic behavior of these materials and clarifies fundamental differences in the electronic dynamics of these two superconducting families.

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Phys. Rev. X 16, 031031– Published 7 August, 2026
  • Received 13 January 2026
  • Accepted 11 June 2026
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