Daily Overview: Today’s highlight work focuses on an in-depth understanding of the electronic structure of mixed Ruddlesden-Popper nickelates. [1] By employing Ni L₃-edge resonant inelastic X-ray scattering, a systematic comparison was made of the spin excitations in the octahedral-phase Nd₉Ni₈O₂₅ (non-superconducting) and its reduced planar-phase counterpart Nd₉Ni₈O₁₈ (with approximately 5 K superconducting correlations). This comparison reveals fundamental differences in the ground state and magnetic excitations between the two structural families: the octahedral phase exhibits a spin-density-wave ground state, whereas the planar phase displays an elastic peak at (1/3,0) with dispersiveless magnetic excitations. These findings provide key experimental evidence for understanding the microscopic mechanism of nickelate superconductivity, highlighting the decisive role of the coordination environment in shaping the electronic structure and superconducting correlations. arXiv submission processing window: 2026-03-30 00:00 to 2026-03-30 00:00 UTC.
1. Contrasting Spin Excitations in Octahedral and Square-Planar n=8 Ruddlesden-Popper Nickelates
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5.1660 - 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
- Link: https://arxiv.org/abs/2603.26593
- Paper page: Contrasting Spin Excitations in Octahedral and Square-Planar n=8 Ruddlesden-Popper Nickelates
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.