Source capture
Authors K. Scott, H. LaBollita, G. A. Pan, X. Yang, A. Kar, C. Lim, A. Thorshov, D. Ferenc Segedin, C. M. Brooks, F. Yakhou-Harris, K. Kummer, N. B. Brookes, F. Boschini, A. Frano, J. A. Mundy, E. H. da Silva Neto, A. S Botana, S. Blanco-Canosa
arXiv / Publisher https://arxiv.org/abs/2603.26593
PDF https://arxiv.org/pdf/2603.26593
Relevance score 5.166
Primary category cond-mat.str-el
Published 2026-03-30
Research paradigm Experimental
Sample form Thin Film

Summary

Using Ni L3-edge resonant inelastic X-ray scattering (RIXS), this study compares low-energy spin excitations in the octahedral Ruddlesden-Popper (RP) phase Nd9Ni8O25 (non-superconducting) and its reduced planar phase Nd9Ni8O18 (exhibiting superconducting correlations at approximately 5 K). The results show that the octahedral phase exhibits a spin-density wave (SDW) ground state with an ordering wave vector of (1/4,1/4), where the low-energy spectrum is dominated by weakly dispersive paramagnons along the (0,π) and (π,π) directions; in contrast, the planar phase displays an elastic peak at (1/3,0) with dispersionless magnetic excitations at an energy of about 65 meV. Polarization-resolved RIXS further confirms the distinct nature of magnetic excitations in the two phases. These findings systematically reveal fundamental differences in the ground states and spin excitations between the two structural families, providing critical insights into the mechanism of nickelate superconductivity.

Materials

Methods

Keywords

Highlights

  • First comprehensive mapping of spin excitations in n=8 RP nickelates using RIXS.
  • Reveals contrasting magnetic ground states between octahedral and square-planar phases.
  • Provides insights for understanding nickelate superconductivity.

Conclusions

  • The octahedral p-RP develops a spin-density-wave ground state with ordering wave vector (1/4,1/4), analogous to bilayer RP.
  • The square-planar r-RP shows an elastic peak at (1/3,0) and dispersionless magnetic excitations.
  • The p-RP exhibits weakly dispersive paramagnons along 0→π and π→π directions, whereas r-RP displays dispersionless magnetic excitations at ≈65 meV.
  • Fundamental differences in ground states and spin excitations between the two structural families are revealed.

Main claims

  • The parent octahedral RP Nd9Ni8O25 develops a spin-density-wave ground state with ordering wave vector q_SDW = (1/4, 1/4).
    • Evidence: Abstract,Full text: The n=8 p-RP develops a spin-density-wave (SDW) ground state with ordering wave vector q_SDW = (1/4, 1/4).
  • The reduced square-planar RP Nd9Ni8O18 shows an elastic peak at q* = (1/3, 0) and dispersionless magnetic excitations near 65 meV.
    • Evidence: Abstract,Full text: the r-RP shows an elastic peak at q* = (1/3, 0) and dispersionless magnetic excitations.
  • The p-RP exhibits weakly dispersive paramagnons along the (0,π) and (π,π) directions, contrasting with the r-RP.
    • Evidence: Abstract,Full text: the p-RP exhibits low-energy spectra dominated by weakly dispersive paramagnons along the (0,π) and (π,π) directions.

Workflow

  • sample_preparation
    • Materials: Nd9Ni8O25; Nd9Ni8O18; NdGaO3 substrate
    • Methods: ozone-assisted molecular beam epitaxy
    • Observations: high-quality thin films
  • RIXS_measurement
    • Methods: Ni L3-edge RIXS; polarimetric RIXS
    • Observations: elastic peaks; inelastic spectra
  • DFT_calculation
    • Methods: WIEN2k (APW+lo); susceptibility calculation
    • Observations: Fermi surface; density of states
  • data_analysis
    • Methods: fits to damped harmonic oscillator
    • Observations: paramagnon dispersion; energy scales
  • interpretation — The p-RP has SDW with q=(1/4,1/4) and weakly dispersive paramagnons; the r-RP lacks long-range order and shows dispersionless magnetic excitations.