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Using first-principles density functional theory calculations, we systematically investigate the electron-doping effects of tetravalent element substitution in double-layer Ruddlesden-Popper nickelate La₃Ni₂O₇ thin films. Unlike cuprates, cerium (Ce) doping is found to be inefficient in introducing electron carriers into low-energy bands, whereas zirconium (Zr), hafnium (Hf), and thorium (Th) serve as effective electron dopants. These elemental substitutions significantly enhance the interlayer hopping integral t⊥ between Ni-dz² orbitals, potentially strengthening the interlayer superexchange coupling J⊥ and thereby potentially increasing the superconducting transition temperature Tc. Using the constrained random phase approximation to evaluate interaction parameters, we find that electron doping increases the occupancy of low-energy orbitals (including Ni-dx²-y² and dz² along with their hybridized oxygen orbitals) and alters the electron filling ratio between in-plane and interlayer orbitals. Structural analysis reveals that differences in dopant ionic radii cause variations in Ni–O bond lengths, with Zr and Hf inducing lattice contraction and Th exhibiting the strongest doping effect. These results indicate that Zr, Hf, and Th are promising candidates for achieving electron doping in La₃Ni₂O₇, offering a new avenue to clarify the ongoing debate over the electron pairing mechanism in this system.

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By combining density functional theory and dynamical mean-field theory, the evolution of the electronic structure, magnetism, and correlation effects in the infinite-layer nickelate LaNiO₂ under electron and hole doping is investigated. The results reveal that, due to the presence of rare-earth 5d states, the self-doping effect of the Ni-d_{x²-y²} band exhibits significant asymmetry: hole doping strongly suppresses self-doping, whereas electron doping, while enlarging the rare-earth 5d electron pocket, does not effectively hole-dope the Ni-d_{x²-y²} band. This difference directly impacts the magnetic response—hole doping rapidly suppresses antiferromagnetic order, while electron doping maintains the antiferromagnetic state as the ground state. Despite these disparities, the electronic correlations in both doping regimes are dominated by the Ni-d_{x²-y²} orbital, suggesting that a single-band description may be applicable in both electron- and hole-doped regions.

Predicting superconducting transition temperature (Tc) remains challenging. This study proposes an interpretable, structure- and chemistry-aware Gaussian process model, GP-Tc, that encodes local bonding environments via graphlet histograms and constructs an effective kernel using Earth mover’s distance, enabling Tc prediction with uncertainty. Analysis shows that Tc across different superconducting families can be predicted using only the distribution of electron affinity differences between adjacent atoms, interatomic distances, and a small number of elemental features, revealing that electron affinity difference is a key chemical parameter linking local bonding to macroscopic superconductivity in a mechanism-agnostic manner. The model reproduces the experimental Tc range of the infinite-layer nickelate Nd0.8Sr0.2NiO2 and predicts superconductivity in stoichiometric PtPb3Bi, which is experimentally confirmed with Tc≈3 K. In addition, GP-Tc is openly accessible through a web interface and identifies high-priority candidate materials such as SrNiO2 and K(PRh)2.

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.

High-temperature superconductivity was discovered in the pressurized nickelate La3Ni2O7 which has a unique bilayer structure and mixed valence state of nickel. The properties at ambient pressure contain crucial information of the fundamental interactions and bosons mediating superconducting pairing. Here, using X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we identified that Ni 3 $${d}_{{x}^{2}-{y}^{2}}$$, Ni 3 $${d}_{{z}^{2}}$$, and ligand oxygen 2p orbitals dominate the low-energy physics with a small charge-transfer energy. Well-defined optical-like magnetic excitations soften into quasi-static spin-density-wave ordering, evidencing the strong electronic correlation and rich magnetic properties. Based on an effective Heisenberg spin model, we extract a much stronger inter-layer effective magnetic superexchange than the intra-layer ones and propose two viable magnetic structures. Our findings emphasize that the Ni 3 $${d}_{{z}^{2}}$$orbital bonding within the bilayer induces novel electronic and magnetic excitations, setting the stage for further exploration of La3Ni2O7 superconductor.

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Trilayer Ruddlesden-Popper phase La4Ni3O10 has been observed with Tc of ∼30 K at high pressure in a recent experiment, which further expanded the family of nickelate superconductors. In this study, we explored the effects of electronic correlations in La4Ni3O10 using density functional theory plus dynamical mean-field theory at ambient and high pressures. Our derived spectral functions and Fermi surface of the ambient pressure phase are nicely consistent with the experimental results by angle-resolved photoemission spectroscopy, which emphasized the importance of electronic correlations in La4Ni3O10. We also found the electronic correlations in pressurized La4Ni3O10 are both orbital-dependent and layer-dependent due to the presence of Hund’s rule coupling. There is a competition between the Hund’s rule coupling and the crystal-field splitting, and therefore, the Ni–O layers with weaker crystal-field splitting energy would have stronger electronic correlations.