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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.

This study systematically characterizes the evolution of unoccupied states in the infinite-layer nickel oxide La₁₋ₓCaₓNiO₂ as a function of doping and temperature using O K-edge and Ni L-edge X-ray absorption spectroscopy. Superconductivity emerges in the doping range of x = 0.18 to 0.27. Near x ≈ 0.20–0.23, a redistribution of low-energy spectral weight occurs: Ni 3d-dominated states decrease while O 2p hybridized states increase, indicating an orbital-selective crossover in Ni–O covalency. This crossover coincides precisely with the sign reversal of the Hall coefficient and precedes the suppression of the superconducting critical temperature at higher doping levels. By directly linking transport anomalies and the superconducting dome to measurable Ni–O orbital reorganization, these results represent a critical step toward establishing a unified orbital-resolved phase diagram for infinite-layer nickelates and offer a practical route for designing superconductivity through hybridization engineering.

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This study reports the transport properties of epitaxial bilayer La₃Ni₂O₇ thin films grown on LaAlO₃(001) and SrLaAlO₄(001) substrates, modulated by high-pressure oxygen annealing and hydrostatic pressure. Under ambient pressure, films on LaAlO₃ substrates exhibit Fermi liquid metallic behavior with a slight Kondo-like upturn at low temperatures; upon applying hydrostatic pressure from 0.53 to 1.41 GPa, the temperature dependence of resistance gradually evolves into non-Fermi liquid behavior, approaching approximately ~T¹⁴ at 1.41 GPa. Notably, this pressure is only 6–8% of that required to achieve similar effects in single crystals using diamond anvil cells, revealing unexpectedly strong tunability in the thin-film form. Additionally, signs of spin-density wave (SDW) order are observed in films on YAlO₃ substrates but suppressed on LaAlO₃ substrates. Hall effect measurements indicate a multiband electronic structure. These results demonstrate that La₃Ni₂O₇ thin films can approach a strongly fluctuating ordered state under moderate pressures, offering a new pathway for studying the origin of non-Fermi liquid behavior and high-pressure superconductivity in thin-film systems.

Using ultrafast optical spectroscopy on La₄Ni₃O₁₀ single crystals, researchers observed an abrupt change in quasiparticle relaxation dynamics at the density-wave transition temperature of approximately 136 K, revealing the opening of a strongly coupled energy gap of about 52 meV. Multiple coherent phonon modes, including Ag modes near 3.88, 5.28, and 2.09 THz, exhibited mode-selective anomalies across the transition, with the renormalization behavior of the 3.88 THz phonon in particular shifting from conventional anharmonic decay at high temperatures to pronounced hardening at low temperatures, indicating strong coupling between the density-wave instability and lattice degrees of freedom and suggesting that electron–phonon interactions likely play a critical role. Under high excitation fluence, the density wave is suppressed non-thermally, yielding a temperature–fluence phase diagram that resembles the pressure-tuning behavior, though the gap remains relatively stable, leading to an increased coupling ratio. These findings establish the density wave in La₄Ni₃O₁₀ as a lattice-entangled instability involving multiorbital physics and confirm that ultrafast photoexcitation can serve as a non-equilibrium control parameter to effectively suppress density-wave order in nickelates.