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Combining a correlated multi-orbital quasiparticle model derived from DFT+CDMFT with the T-matrix method, this study treats oxygen vacancy scattering within a semiclassical Boltzmann transport framework and reveals the microscopic origin of the Hall coefficient sign reversal in bilayer nickelate thin films. Multiband compensation alone is insufficient to explain the phenomenon; in-plane oxygen vacancies strongly suppress the transport channel dominated by the d_{x^2-y^2} orbital through orbital-selective scattering, driving the Hall coefficient across zero to become positive, whereas apical oxygen vacancies tend to make the Hall coefficient more negative. This pocket-resolved and orbital-selective scattering mechanism demonstrates that oxygen vacancies act not only as electron doping sources but also as active scattering centers whose spatial distribution directly controls the normal-state transport behavior, providing a theoretical framework for a unified understanding of the diverse Hall responses observed experimentally as a function of oxygen stoichiometry.

2 linked papers

2 linked papers

This study reports the first successful synthesis of heavily Sr-doped La₂SrNi₂O₇₋δ single crystals by a high-pressure, high-temperature flux method. X-ray diffraction and scanning transmission electron microscopy confirm that the material adopts a tetragonal I4/mmm structure at ambient pressure, with a Ni−O−Ni bond angle of 180° along the c-axis, indicating that heavy doping effectively suppresses the distortion of NiO₆ octahedra. Resistivity measurements reveal metallic behavior with a low-temperature upturn, and no density-wave features are observed; however, neither applying pressure nor varying the oxygen content induces superconductivity. Density functional theory calculations show that holes introduced by Sr doping predominantly enter the Ni-3d_z² orbital, creating a large γ pocket on the Fermi surface and markedly reducing the occupation of this orbital, so that the Ni-3d_z² band deviates strongly from half-filling. The authors accordingly argue that this departure from half-filling weakens interlayer antiferromagnetic interactions and pairing, which is the key reason superconductivity does not emerge in this system. This work provides important clues for understanding the conditions required to realize superconductivity in bilayer nickelates.

This study proposes a novel route to electron doping in nickelate superconductors through heterostructuring. First-principles calculations reveal that upon inserting wide-bandgap insulating layers of LaXO₃ (X = Al, Ga, Sc) into La₂NiO₄, the additional (LaO)⁺ layers act as electron donors, releasing carriers into the Ni-3d orbitals and thereby achieving disorder-free electron doping of Ruddlesden–Popper nickelates. This doping naturally places La₂NiO₄:La₂AlO₄ in the optimal regime for d_{x^2−y^2}-wave superconductivity, with many-body methods—including dynamical vertex approximation, fluctuation exchange, and dynamical cluster approximation—predicting a superconducting critical temperature exceeding 50 K and reaching as high as 127 K. The strategy circumvents the disorder typically introduced by conventional chemical doping, and is equally applicable to other nickelates such as La₃Ni₂O₇, offering a viable scheme for comprehensively mapping the electron-doping phase diagram of nickelates and extending the approach to other transition metal oxide systems.

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This study employs the variational Monte Carlo method to perform nonperturbative calculations on a bilayer two-orbital Hubbard model, revealing the hierarchical structure of superconducting pairing in the bilayer layered nickelate La₃Ni₂O₇. It is found that the primary pairing interaction originates from the bonding-anti-bonding splitting of the Ni 3d({z^2}) orbital, while orbital hybridization redistributes superconducting correlations into the 3d({x^2-y^2}) channel, despite its intrinsically weak pairing interaction. This distinction between the origin of pairing and the source of superconducting correlations explains why both orbital channels exhibit comparable long-range superconducting correlations, and the resulting s± state is robust against changes in Fermi surface topology, such as the disappearance of the α Fermi pocket. The results reconcile previously divergent theoretical perspectives on the pairing mechanism, indicating that the strength of superconducting correlations is primarily determined by the orbital character of the low-energy density of states, whereas the pairing interaction stems from orbital level splitting in the bilayer structure, highlighting the crucial role of orbital hybridization in stabilizing superconductivity in multilayer layered superconductors.

High oxygen pressure floating zone growth and crystal structure of the metallic nickelates R₄Ni₃O₁₀ ( R = La, Pr )