Daily Overview: Today’s highlights focus on deepening the understanding of the electronic structure of hybrid Ruddlesden-Popper nickelates. A series of experimental and theoretical studies, spanning strain engineering, high-pressure phase diagrams, pairing symmetry, and multi-orbital density waves, reveal the unique roles of orbital selectivity and unconventional pairing mechanisms in nickel-based superconductors. In La₂PrNi₂O₇ thin films, an extreme compressive strain of up to –2.14% achieves an onset superconducting transition at 60 K, and the Hall effect exhibits electron-like carrier character, in stark contrast to the hole-like behavior observed in the bulk under high pressure, highlighting the potential of strain tuning to transcend limits imposed by Fermi surface topology. Pressure-evolution calculations for La₃Ni₂O₇ indicate that enhanced interlayer hopping and Kondo screening jointly suppress the effective magnetic exchange coupling, providing a self-consistent picture for the dome-shaped pressure dependence of the superconducting transition temperature. Concurrently, theory based on a bilayer t-J model reproduces the s± pairing-dominated nodeless gap structure and a critical temperature of about 60 K in films, and points out that d-wave pairing components among multiple orbitals can further enhance superconductivity. Ab initio calculations on infinite-layer nickelates establish spin-fluctuation-driven d_(x²−y²)-wave pairing and predict nodal-line gap features awaiting experimental verification. Polarization-resolved Raman scattering on the trilayer nickelate La₄Ni₃O₁₀ directly observes the incoherent opening of a density-wave gap and confirms that this instability intrinsically originates from the mixed contributions of the Ni-3d_(x²−y²) and 3d_(z²) orbitals. Moreover, free-standing La₀.₈Sr₀.₂NiO₂ films exhibit a dome-shaped superconducting phase diagram under ultra-high pressure up to 210 GPa, with the onset temperature rising to 74.5 K at 146 GPa, indicating that the NiO₂ plane can sustain anomalously robust pairing strength under extreme compression and is almost unaffected by rare-earth magnetic moments. Collectively, these results enrich the multi-orbital physical picture of nickelate superconductivity and provide crucial experimental and theoretical foundations for exploring new dimensions of high-temperature superconductivity. arXiv submission processing window: 2026-08-04 00:00 to 2026-08-04 00:00 UTC.

1. Electron-like high-temperature superconductivity induced by compressive strain in La2PrNi2O7 thin films

Summary: Using ozone-assisted atomic layer epitaxy, the researchers grew La2PrNi2O7 thin films on NdAlO3 substrates, introducing an extreme compressive strain of up to −2.14% and achieving high-temperature superconductivity with an onset critical temperature of 60 K, a zero-resistance temperature of 33 K, and a diamagnetic transition at 20 K, while magnetotransport measurements confirmed a quasi-two-dimensional superconducting state. A comparison of the phase diagrams between the strained films and high-pressure bulk materials reveals that, although both suppress spin-density waves to drive superconductivity, the lattice responses diverge: the film’s c-axis parameter window markedly departs, whereas the in-plane parameters coincide with those of the bulk. Crucially, Hall measurements uncover a dichotomy in electronic character, as the optimal superconducting film exhibits a negative Hall coefficient indicative of electron-like behavior, in stark contrast to the positive, hole-like Hall coefficient of high-pressure bulk samples and non-superconducting tensile-strained films. These observations indicate that both strain and pressure strategies effectively tune the underlying correlation modulation beyond the constraints of a specific Fermi surface topology, thereby enabling superconductivity. This work establishes a macroscopic platform for studying multi-orbital physics in nickelates and provides a new dimension for exploring the mechanism of high-temperature superconductivity.

2. Pressure-Driven Evolution of Electronic and Magnetic Correlations in Bilayer Nickelate La3Ni2O7

Summary: Using a combination of density functional theory, constrained random phase approximation, and dynamical mean-field theory, we systematically investigate the evolution of electronic and magnetic correlations in the bilayer nickelate La₃Ni₂O₇ under pressure. Our calculations show that hydrostatic pressure enhances interlayer hopping and the bare superexchange energy scale, while reducing the relative correlation strength U/W, driving the system overall towards an itinerant state. Crucially, a clear orbital-selective evolution is observed: the Ni dx²-y² orbital becomes increasingly itinerant, whereas the Ni dz² orbital retains strong localization; pressure enhances their hybridization, greatly amplifying the Kondo screening effect of itinerant electrons on the localized magnetic moments. Consequently, the effective magnetic exchange coupling that mediates pairing is suppressed in the high-pressure regime, indicating that the monotonic decrease of the superconducting transition temperature under high pressure arises from Kondo screening overwhelming the superexchange interaction, and thus providing a self-consistent microscopic explanation for the dome-shaped superconducting phase diagram of La₃Ni₂O₇.

3. Pairing symmetry and superconductivity in La$_3$Ni$_2$O$_7$ thin films

Summary: Using renormalized mean-field theory based on a bilayer (t-J) model incorporating (d_{z^2}) and (d_{x^2-y^2}) orbitals, this study systematically investigates the superconducting pairing symmetry of La₃Ni₂O₇ thin films. Self-consistent solutions reveal (s_\pm)-wave pairing driven by strong interlayer superexchange coupling of the (d_{z^2}) orbital, consistent with the pressurized bulk case, and successfully reproduce the nodeless superconducting gap structure on the (\beta) Fermi surface pocket observed by angle-resolved photoemission spectroscopy, yielding a calculated superconducting transition temperature of approximately 60 K in agreement with experiments. Orbital-resolved analysis demonstrates that the nodeless character of the (\beta) pocket arises from the cooperative interlayer pairing of (d_{z^2}) and (d_{x^2-y^2}) orbitals, while in-plane pairing between these orbitals generates a (d)-wave component that further enhances the dominant (s_\pm)-wave order. The work elucidates the diverse cooperative and competitive relationships among different pairing channels on the complex Fermi surfaces of La₃Ni₂O₇ films and discusses the potential modulation of pairing symmetry by factors such as substrate strain and oxygen vacancies, providing a crucial theoretical basis for understanding the superconducting mechanism in nickelates.

4. {\it Ab initio} prediction of $d_{x^2-y^2}$-wave superconductivity in infinite-layer nickelates

Summary: This study employs superconducting density functional theory to perform ab initio calculations on optimally doped infinite-layer nickelates Re₀.₈Sr₀.₂NiO₂ (Re=La, Pr, Nd), treating electron–phonon coupling, screened Coulomb repulsion, and spin fluctuations on an equal footing. The results reveal that these materials are two-band superconductors exhibiting opposite-sign d_(x²−y²)-wave pairing gaps on different Fermi surfaces; when spin fluctuations are switched off, the critical temperature drops to a negligible ~0.01 K, indicating that superconductivity is driven by spin fluctuations. On the large quasi-two-dimensional Fermi surface at the Brillouin zone center, the spin fluctuation strength is an order of magnitude larger than that of electron–phonon coupling and Coulomb repulsion, thereby dominating the pairing mechanism, whereas electron–phonon coupling plays the principal role on the small three-dimensional electron pockets at the zone corners. The nodal d-wave gap structure originates from a pronounced peak of the Lindhard response function at the zone corners. The calculated Fermi surfaces, critical temperature, nodal gaps, and quasiparticle density of states are in agreement with most experimental observations, and the predicted unconventional superconducting properties such as scanning tunneling spectra await direct experimental verification.

5. Multiorbital character of the density wave in trilayer nickelate superconductors

Summary: Using polarization-resolved Raman scattering combined with a two-orbital model calculation, this study reveals the multi-orbital character of the density wave in the trilayer nickelate La4Ni3O10. In the phonon sector, the oxygen bond-stretching mode exhibits a pronounced intensity anomaly near the density-wave transition temperature T_DW, while the phonon line shape remains essentially symmetric with negligible changes in frequency shift and linewidth, indicating a moderate electron-phonon coupling and suggesting that the density wave is primarily driven by electronic instability rather than by the lattice. In the electronic Raman scattering, as temperature decreases, the spectral weight of the continuum is significantly depleted below ∼114 meV (∼910 cm⁻¹), and a polarization-dependent sharp peak emerges at this energy; this peak is strongest in the B₂g channel and nearly absent in the B₁g channel. By constructing a two-orbital density-wave state model that simultaneously includes Ni-3d_{x²−y²} and Ni-3d_{z²} orbitals and retains the Raman vertices in the orbital space, calculations confirm that this peak corresponds to the density-wave energy gap 2Δ_DW, whose opening displays incoherent and non-mean-field behavior, and that the spectral response necessarily relies on the mixed contributions of both orbitals and cannot be reduced to any single-orbital projection. These results demonstrate that the density-wave instability in La4Ni3O10 has an intrinsic multi-orbital origin, providing crucial experimental and theoretical insights for understanding its competition or coexistence with superconductivity.

6. Enhanced and robust superconductivity in La0.8Sr0.2NiO2 membranes compressed up to 210 GPa

Summary: Researchers have prepared freestanding La₀.₈Sr₀.₂NiO₂ thin films and performed electrical resistance measurements using a diamond anvil cell at ultrahigh pressures up to 210 GPa. The experiments reveal a dome-shaped evolution of the superconducting onset transition temperature: beginning at approximately 16 K at ambient pressure, it rises monotonically with increasing pressure, reaches a peak of 74.5 K at 146 GPa, and then slowly decreases while still retaining 57.4 K at 210 GPa. Through derivative analysis and magnetic field suppression experiments, it is confirmed that this enhancement in transition temperature stems from an intrinsic strengthening of superconductivity, rather than a simple broadening of the transition width. A comparison with Nd₀.₈₅Sr₀.₁₅NiO₂ films shows that both exhibit a linear increase with pressure below 60 GPa with similar slopes, though their behaviors diverge at higher pressures; nonetheless, the maximum onset temperature for both is approximately 75 K, indicating that the NiO₂ planes dominate the superconductivity and that the magnetic moments of rare-earth f orbitals have minimal influence. This work represents the first observation of robust superconductivity in oxide superconductors over such a wide pressure range, demonstrating that the pairing strength in infinite-layer nickelates remains unsuppressed under extreme compression, and provides important clues for understanding the mechanism of unconventional superconductivity.