Daily Overview: Today’s highlights focus on deepening the understanding of the electronic structure of hybrid Ruddlesden-Popper nickelates. [1] Based on a bilayer t-J model, the modulation of superconducting transition temperature by oxygen stoichiometry, elemental substitution, pressure, and strain in La₃Ni₂O₇ is explained in a unified manner, indicating that electron doping is a potential route to enhance Tc. [2] High-precision transport measurements reveal the critical role of interlayer electronic coherence in Ruddlesden-Popper nickelates: stronger interlayer coherence favors superconductivity, and the out-of-plane resistivity serves as a sensitive probe of magnetic and density-wave orders, providing strict constraints on the microscopic mechanism of superconductivity. [3] Combining first-principles calculations with dynamical cluster quantum Monte Carlo simulations, it is predicted that electron doping can universally enhance s±-wave superconductivity in La₃Ni₂O₇, with heterostructure systems exhibiting the highest Tc in the underdoped regime, and revealing a cooperative pairing mechanism between dz² and dx²-y² orbitals. arXiv submission processing window: 2026-05-19 00:00 to 2026-05-19 00:00 UTC.

1. A Unified Understanding of the Experimental Controlling of the T$_\text{c}$ of La$_3$Ni$_2$O$_7$

Summary: Based on the previously proposed effective d_{x^2-y^2}-orbital bilayer t-J_∥-J_⊥ model with parameters derived from first-principles calculations, this work provides a unified explanation for experiments tuning the superconducting transition temperature of La₃Ni₂O₇ through oxygen stoichiometry, elemental substitution, pressure, or strain. The model, near quarter filling, exhibits Tc tuning behavior analogous to that of hole-doped overdoped cuprates: hole (electron) doping renders the system more (less) overdoped and suppresses (enhances) Tc, thereby explaining the experimental observations that increasing oxygen stoichiometry or substituting Ca²⁺/Sr²⁺ for La³⁺ introduces hole doping and suppresses Tc, as well as the “half-dome” behavior in oxygen stoichiometry tuning. Regarding interaction dependence, Tc varies with interlayer antiferromagnetic superexchange J_⊥, consistent with the enhancement of bulk Tc by Sm/Nd substitution for La, the “right-triangle” relationship between bulk Tc and pressure, and the enhancement of Tc in thin films under compressive strain. Compared with weak-coupling theories (where Tc primarily depends on the density of states) and d_{z²}-orbital-dominated pairing mechanisms (where Tc is proportional to the d_{z²} hole density), this model offers a more natural and unified explanation for the experiments. The authors propose that electron doping via substitution of La with higher-valent elements, without introducing disorder, has the potential to raise Tc.

Summary: This study employed the six-terminal method to perform high-precision transport measurements on Ruddlesden–Popper nickelate bilayer and trilayer single crystals, self-consistently extracting the in-plane and out-of-plane resistivities. The results reveal strong intrinsic electronic anisotropy, with out-of-plane resistivity exhibiting a non-monotonic temperature dependence that signals a universal interlayer coherent-to-incoherent crossover. Under pressure, the maximum superconducting transition temperature is inversely proportional to the resistivity anisotropy at ambient pressure, indicating that stronger interlayer electronic coherence favors superconductivity. Moreover, out-of-plane resistivity serves as a sensitive probe of magnetic and density-wave orders, whereas the in-plane resistivity shows a weaker response. These findings highlight interlayer coherence as a key tuning parameter that both tracks magnetic correlations and is closely linked to superconductivity, providing stringent constraints for microscopic theories of nickelate high-temperature superconductivity.

3. Enhanced $s^\pm$-wave superconductivity in electron-doped La$_3$Ni$_2$O$_7$

Summary: This study systematically investigates the effect of electron doping on the s±-wave superconducting properties of three representative systems—bulk La₃Ni₂O₇ at ambient pressure and 15 GPa, as well as the electron-dopable heterostructure La₃Ni₂O₇:La₃Al₂O₇—using first-principles calculations and large-scale dynamical cluster quantum Monte Carlo simulations. The results reveal that electron doping universally enhances s±-wave pairing superconductivity in all three systems, with the heterostructure exhibiting the highest superconducting transition temperature in the underdoped regime. Analysis of orbital-resolved pairing susceptibilities and eigenvectors uncovers an inter-orbital cooperation mechanism: pairing in the d_z² orbital induces pairing in the d_{x²-y²} orbital, which dominates superconductivity at low temperatures. This work predicts enhanced superconductivity in electron-doped Ruddlesden–Popper nickelates and provides a theoretical foundation for future experimental verification.