Daily Overview: Today’s highlighted work centers on an in-depth understanding of the electronic structure of hybrid Ruddlesden–Popper nickelates. On the one hand, a theoretical study proposes a dual‑parameter control framework based on in‑plane d_(x²–y²) orbital filling and effective interlayer antiferromagnetic superexchange, providing a unified explanation for the systematic variation of the superconducting transition temperature in the bilayer nickelate La₃Ni₂O₇ under pressure, composition, and strain. It explicitly indicates that clean electron doping can enhance pairing strength, whereas oxygen vacancies suppress superconductivity by disrupting exchange pathways and inducing disorder effects. On the other hand, a high‑pressure single‑crystal structural investigation of the trilayer nickelate La₄Ni₃O₁₀ clarifies its direct transition path from the tetragonal to the monoclinic phase, reveals that pressure effectively stabilizes tetragonal symmetry, and detects faint structural distortions associated with density‑wave order. These findings provide key crystallographic evidence for the consensus that superconductivity emerges upon restoring the tetragonal phase under high pressure. Together, these two studies—from theory and experiment—deepen our understanding of the cooperative interplay among charge, spin, and lattice degrees of freedom in nickelates, and jointly point to a viable strategy for optimizing superconducting properties by controlling interlayer coupling and structural symmetry. arXiv submission processing window: 2026-07-16 00:00 to 2026-07-16 00:00 UTC.

1. Filling and Interlayer Superexchange Control Superconductivity in La$_3$Ni$_2$O$_7$

Summary: This work proposes a unified two-parameter control principle centered on the in-plane d_(x²–y²) orbital filling n_x and the effective interlayer antiferromagnetic superexchange J⊥ to explain the systematic response of the superconducting transition temperature T_c in the bilayer nickelate superconductor La₃Ni₂O₇ to pressure, strain, oxygen stoichiometry, and chemical substitution. Starting from first-principles-constrained parameters, an effective single-orbital bilayer t–J⊥ model is constructed and studied using slave-boson mean-field theory and density matrix renormalization group methods. Calculations reveal that actual La₃Ni₂O₇ resides in an overdoped cuprate-like regime where T_c is primarily determined by the pairing energy scale; in this regime, hole doping reduces n_x and suppresses T_c, whereas tuning knobs that enhance J⊥ raise T_c. This framework unifies the suppression caused by oxygen overdoping and Ca/Sr substitution, the half-dome-like response of T_c with oxygen stoichiometry in thin films, the enhancements from Nd/Sm substitution and optimal pressure in bulk materials under high pressure, the pressure-dependent right-triangle-shaped T_c curve, and the boosting effect of compressive strain in films. The study further distinguishes clean carrier doping from oxygen-vacancy control: clean electron doping principally increases n_x and strengthens the pairing scale, whereas oxygen vacancies disrupt the apical-oxygen-mediated exchange pathway and introduce disorder, rendering them not equivalent to simple doping. A testable material design prediction emerges — that clean electron doping, under conditions that avoid oxygen vacancies and strong pair-breaking disorder, should enhance pairing strength, providing a clear guideline for optimizing superconductivity in nickelates.

2. Tracing the horizon of tetragonal-to-monoclinic distortion in pressurized trilayer nickelate La4Ni3O10

Summary: This study employs pressure-temperature single-crystal X-ray diffraction and ab initio density functional theory calculations to reveal that the transition from the tetragonal phase (I4/mmm) to the monoclinic phase (P2₁/c) in flux-grown trilayer nickelate La₄Ni₃O₁₀ does not involve an intermediate orthorhombic Bmab phase; instead, it is a direct structural phase transition accompanied by the formation of a two-fold superstructure, manifested by the appearance of commensurate superlattice reflections. The transition temperature can be continuously suppressed from approximately 1030 K to 20 K under a pressure of 14 GPa, indicating that pressure effectively stabilizes the tetragonal phase. Furthermore, weak satellite reflections associated with incommensurate density wave ordering are detected for the first time in X-ray diffraction from flux-grown crystals, complementing previous results observed only in float-zone crystals, and Raman spectroscopy reveals additional phonon modes below 130 K, further corroborating this ordered state. The ab initio calculations are in good agreement with the experimental observations. This work clarifies the long-standing dispute over the structural symmetry of La₄Ni₃O₁₀, supports the emergence of superconductivity after the restoration of tetragonal symmetry under high pressure, and provides a critical crystallographic foundation for subsequent studies of electronic structure and superconducting mechanisms.