Daily Overview: Today’s highlights focus on a deeper understanding of the electronic structure of mixed Ruddlesden–Popper nickelates. Specifically, [1] achieved tuning of c-axis uniaxial pressure and interlayer coupling in bilayer nickelate thin films via ozone annealing and isovalent rare-earth A-site substitution; upon optimizing superconductivity, the SDW transition temperature decreases from 150 K to 70 K. Although the SDW is weakened, it still persists, whereas the charge-like anisotropic order is completely eliminated in the superconducting state. Polarization-resolved O K-edge XAS and electronic structure calculations indicate that enhanced interlayer Ni–O–Ni hybridization can reconstruct the Fermi surface and suppress magnetic fluctuations near the SDW wavevector, indicating that the two electronic orders are governed by different energy scales and are consistent with the spin–spinless stripe ground-state picture. Meanwhile, [2] systematically investigated the electronic structure of four-layer La5Ni4O13 under ambient pressure, isotropic compression, and c-axis uniaxial strain using DFT+RPA, constructing a four-layer two-orbital model. This revealed that isotropic strain induces bandwidth broadening and O-p→Ni-d charge transfer, whereas c-axis compression selectively shifts d_{z^2}-derived bands upward and generates γ hole pockets; the dominant spin response shifts from q≈(2π/3,2π/3) to q≈(π,π) and is enhanced under c-axis compression, suggesting that c-axis compression may provide a favorable superconducting pathway for four-layer nickel oxides similar to bilayer/trilayer systems. Together, these results highlight the key regulatory role of interlayer coupling and lattice strain in the density-wave and superconducting phase diagrams of nickelates. arXiv submission processing window: 2026-10-02 00:00 to 2026-10-02 00:00 UTC.

1. Selective suppression of electronic orders via interlayer coupling in superconducting bilayer nickelate thin films

Summary: This study investigates the interplay of spin density wave (SDW) and charge-anisotropy-like order with superconductivity in bilayer nickelate films by combining ozone annealing and isovalent rare-earth A-site substitution to effectively apply c-axis uniaxial pressure and tune interlayer coupling. Resonant elastic X-ray scattering shows that, upon optimizing superconductivity, the SDW transition temperature decreases from 150 K to 70 K; although weakened, the SDW persists, whereas the charge-anisotropy-like order is completely eliminated in the superconducting state. Polarization-resolved O K-edge X-ray absorption spectroscopy and electronic structure calculations indicate that both the c-axis compression induced by A-site substitution and the filling of interlayer oxygen vacancies by ozone annealing enhance interlayer Ni-O-Ni hybridization, reconstruct the Fermi surface, and suppress magnetic fluctuations near the SDW wave vector, thereby weakening the SDW instability. These results indicate that the two electronic orders are governed by different energy scales and are consistent with a spin–spinless stripe ground state, providing new clues for understanding density-wave formation and its relationship to superconductivity in bilayer nickelates.

2. Electronic structure and two-orbital model of the quadlayer La$_5$Ni$_4$O$_{13}$

Summary: Using density functional theory (DFT) and random phase approximation (RPA) calculations, we systematically investigated the electronic structures of the four-layer Ruddlesden–Popper nickelate La5Ni4O13 under ambient pressure, 5% isotropic compressive strain, and 4% c-axis uniaxial strain, and constructed a four-layer two-orbital model based on Wannier downfolding. DFT shows that isotropic strain broadens the Ni-e_g bands and induces charge transfer from O-p to Ni-d, whereas c-axis uniaxial strain selectively shifts the d_z2-derived bonding1 band upward while leaving the d_x2-y2 dispersion almost unchanged. The two-orbital model reproduces the low-energy Ni-e_g bands. Under ambient pressure and 5% isotropic strain, the Fermi surface consists of two electron pockets (α, δ) and three hole pockets (β, β′, β″); under uniaxial strain, a γ hole pocket with d_z2 orbital character emerges. RPA calculations show that the dominant spin response changes from q≈(2π/3,2π/3) at ambient pressure to q≈(π,π) under both strains, and is enhanced under c-axis compression. The authors therefore suggest that c-axis compression may provide four-layer nickelates with a favorable superconducting pathway similar to those of bilayer and trilayer nickelates.