Daily Overview: Today’s highlights focus on deepening the understanding of the electronic structure of hybrid Ruddlesden–Popper nickelates. Two resonant inelastic X‑ray scattering studies reveal, from the perspectives of doping and strain respectively, the intrinsic connection between spin excitations and superconductivity in bilayer nickelates: in La₃₋ₓSrₓNi₂O₇ thin films, beyond the superconducting dome, coherent spin excitations undergo magnetic collapse, with their quenching occurring concurrently with the reconstruction of the apical‑oxygen‑mediated d_(z²)–p_z–d_(z²) orbitals, clearly indicating that maintaining a local d_(z²) magnetic structure and robust interlayer apical‑oxygen coupling is a fundamental prerequisite for achieving high‑temperature superconductivity. Meanwhile, strain engineering of La₃Ni₂O₇ thin films demonstrates that compressive strain enhances the interlayer antiferromagnetic superexchange J_z accompanied by the emergence of superconductivity, while tensile strain markedly suppresses spin excitations and d_(z²)‑related excitations, providing direct spectroscopic evidence for the theoretical picture of pairing promoted by interlayer antiferromagnetic superexchange. In addition, a first‑principles calculation reveals a unique bipartite electronic system in a new bilayer nickel oxide, La₃Ni₂O₅F, where conventional Ni dpσ hole carriers coexist with E* electron carriers originating from interstitial electronic states, forming a cylindrical electron Fermi surface and velocity‑parallel potential Dirac points. This two‑component electronic configuration is expected to induce unconventional superconducting behavior, offering a possible route toward new designs of apical‑oxygen‑free nickelate superconductors. arXiv submission processing window: 2026-06-10 00:00 to 2026-06-10 00:00 UTC.

1. Doping evolution of spin excitations in La$_{3-x}$Sr$_{x}$Ni$_2$O$_7$/SrLaAlO$_4$ superconducting thin films

Summary: This study employs Ni L3-edge resonant inelastic X-ray scattering to systematically trace the evolution of spin and electronic excitations with hole doping in La3-xSrxNi2O7/SrLaAlO4 superconducting thin films. In the superconducting regime (x ≤ 0.21), dispersive spin excitations characterized by double-stripe correlations and a nearly doping-independent exchange energy scale persist robustly. However, upon entering the overdoped non-superconducting state (x = 0.38), this coherent magnetic structure abruptly collapses into a heavily damped, low-spectral-weight continuum. It is found that this magnetic collapse is primarily driven by a selective doping-induced orbital reconstruction: the 1.0 eV intra-atomic dd peak remains unchanged, indicating an intact local octahedral crystal field, whereas the simultaneous quenching of the ~0.4 eV and ~1.6 eV features signals a severe degradation of both the d_{z^2}–p_z–d_{z^2} singlet sector mediated by apical oxygen and the bilayer charge-transfer coherence. The concurrent demise of coherent spin excitations and macroscopic superconductivity establishes a direct doping-tuned link, unequivocally revealing that maintaining a local d_{z^2} magnetic structure and robust apical-oxygen coupling is a fundamental prerequisite for realizing high-temperature superconductivity in bilayer nickelates.

2. Spin correlations in La$_3$Ni$_2$O$_7$ thin films

Summary: This study employs resonant inelastic X-ray scattering (RIXS) to systematically investigate the electronic and spin excitation properties of La₃Ni₂O₇ thin films under different epitaxial strains. In a compressively strained (ε ≈ −2%) LNO/SLAO film, dispersive spin excitations resembling those of the bulk material are observed but exhibit a larger bandwidth and enhanced interlayer exchange coupling J_z; in contrast, spin excitations and Ni 3d_(z²)-related dd excitations are both markedly suppressed in a tensile-strained (ε ≈ +1.9%) LNO/STO film. These changes reflect effective tuning of the interlayer exchange interaction J_z and the Ni 3d_(z²)–O 2p_z hybridization by epitaxial strain. The results demonstrate that epitaxial strain, through modulation of the Ni–O–Ni bond angle and c-axis length, significantly affects interlayer antiferromagnetic superexchange interactions, and that the enhanced J_z is closely correlated with the onset of ambient-pressure superconductivity, providing direct spectroscopic evidence for the theoretical scenario of interlayer antiferromagnetic superexchange promoting pairing in bilayer nickelates.

3. Dichotomous electronic system in a bilayer Ni$^{1+}$ nickelate

Summary: Through first-principles calculations, this study investigates the electronic structure of a novel bilayer nickelate, La₃Ni₂O₅F. This material exhibits infinite-layer nickelate characteristics, with Ni ions in the Ni¹⁺ oxidation state and lacking apical oxygens; its blocking layers isolate the NiO₂ bilayers, rendering the system ideally two-dimensional. The calculations reveal a partially occupied E* band originating from interstitial electronic states, which extends out-of-plane across three “apical” layers, forming a cylindrical electron Fermi surface and self-doping approximately 0.18 electrons into the dpσ hole band. The interstitial states couple with the Ni d_{xz/yz} orbitals, producing parallel bands with identical velocity and linearity near the M point, potentially forming nonanalytic Dirac points. The d_{z²} orbital is split by about 1 eV due to coupling through the interstitial density. This system exhibits dual quantum particle behavior: coexistence of conventional Ni dpσ hole-type carriers and interstitial E* electron-type carriers, leading to two-component behavior in normal-state transport and far-infrared properties, and possibly inducing unconventional superconductivity.