Daily Overview: Today’s highlighted work focuses on an in-depth understanding of the electronic structure of hybrid Ruddlesden-Popper nickelates. Two studies, based respectively on experimental spectroscopy and first-principles many-body calculations, reveal the key influence of layer configuration and Ni–O hybridization on magnetic excitations, electron–phonon coupling, and superconducting pairing symmetry. In one study, comparison of two polytypes of La3Ni2O7 and La4Ni3O10 using Ni L3-edge and O K-edge resonant inelastic X-ray scattering reveals that the electronic, magnetic, and lattice excitations of LNO-1313 and La4Ni3O10 are highly similar, whereas bilayer LNO-2222 exhibits stronger orbital polarization, weaker 3d^8L ligand-hole character, larger out-of-plane magnetic exchange, and weaker electron–phonon coupling, thus providing important experimental constraints for low-energy theoretical models of layered nickelate superconductors. The other DFT+RPA study shows that, within a full-spectrum projected model that preserves the density functional theory band structure, Ni–O hybridization significantly enhances interlayer spin fluctuations and generates a commensurate magnetic instability, thereby stabilizing a sign-changing s±-wave superconducting state. By contrast, a Wannier model that describes only the low-energy bands near the Fermi surface tends to favor d-wave pairing, indicating that the interlayer coupling and Ni–O hybridization included in a full-energy description play an important stabilizing role in theoretical predictions of the pairing symmetry of bilayer nickelates. arXiv submission processing window: 2026-09-07 00:00 to 2026-09-07 00:00 UTC.

1. Layer Architecture Shapes Electronic, Magnetic, and Lattice Interactions in Ruddlesden-Popper Nickelates

Summary: We performed a systematic comparison of the two polytypes of La3Ni2O7—the alternating monolayer-trilayer LNO-1313 and the bilayer LNO-2222—and the trilayer compound La4Ni3O10 using Ni L3-edge and O K-edge resonant inelastic X-ray scattering (RIXS). We find that the electronic, magnetic, and lattice excitations of LNO-1313 and La4Ni3O10 are highly similar, whereas bilayer LNO-2222 exhibits distinctly different features. Compared with LNO-2222, LNO-1313 and La4Ni3O10 possess weaker orbital polarization, enhanced 3d^8 L (ligand-hole) character, a smaller out-of-plane magnetic exchange scale, and stronger electron-phonon coupling. Within an effective local-moment framework, the spin excitations arising from strong antiferromagnetic interlayer coupling can be naturally described by an entangled-dimer picture, whose advantage is most evident in bilayer LNO-2222, where the interlayer coupling exceeds the intralayer interactions. These results provide key experimental constraints for theoretical models of the low-energy physics relevant to superconductivity in layered nickelates.

2. Ni-O hybridization as a stabilizer for $s^{\pm}$ superconductivity in La$_3$Ni$_2$O$_7$: a DFT+RPA study

Summary: This study addresses the controversy over the superconducting pairing symmetry of the high-pressure bilayer nickelate La₃Ni₂O₇ by employing a full-spectrum model based on orthogonalized projection (the Oroj method), which projects Kohn–Sham states onto local Ni-e_g orbitals and, while preserving the density functional theory band structure, redistributes spectral weight over a wider energy range, thereby incorporating Ni–O hybridization and contributions from electronic states away from the Fermi surface. Compared with a Wannier model that describes only the low-energy bands near the Fermi surface, this full-spectrum model significantly enhances interlayer spin fluctuations and yields a commensurate magnetic instability; within the spin-fluctuation framework, such features favor the formation of a sign-changing s±-wave superconducting state, whereas the low-energy model tends toward d-wave pairing. The results indicate that interlayer coupling and Ni–O hybridization in the full-energy description play an important stabilizing role in theoretical predictions of the superconducting pairing symmetry of bilayer nickelates.