Daily Overview: Today’s highlighted work focuses on a deeper understanding of the electronic structure of mixed-type Ruddlesden–Popper nickelates. For La3Ni2O7+δ, researchers tuned the oxygen content by annealing and showed that it not only alters the NiO6 octahedral distortion and the proportions of bilayer, mixed-phase, and trilayer intergrown phases but also directly determines the superconducting transition temperature and upper critical field; they further established phase diagrams for the evolution of Tc and Hc2 with oxygen content. On the theoretical side, sign-problem-free determinant quantum Monte Carlo studies demonstrate that a two-orbital model of bilayer nickelates can realize spin-singlet, layer-triplet superconductivity, whose stability is jointly governed by doping, Hund’s coupling, and interlayer tunneling; under strong correlations, the accompanying (π,π) interlayer bond order may be related to the mysterious density wave observed experimentally. Moreover, X-ray absorption spectroscopy and resonant inelastic X-ray scattering on trilayer Pr4Ni3O10 resolve multiorbital anisotropy and magnetic excitation softening near the incommensurate spin-density-wave wavevector, indicating that intra-trilayer exchange coupling is significant and insensitive to rare-earth substitution, thereby highlighting the tuning role of multilayer structures in magnetic interactions. Overall, today’s work advances the understanding of nickelate superconductors and related Ruddlesden–Popper nickelates from three aspects: oxygen stoichiometry, pairing mechanism, and magnetic excitations. arXiv submission processing window: 2026-10-08 00:00 to 2026-10-08 00:00 UTC.

1. Regulating oxygen content and superconductivity in La$_3$Ni$_2$O$_{7+δ}$

  • Relevance Score: 5.6657
  • Authors: Peiyue Ma, Jingyuan Li, Xing Huang, Yixing Zhao, Yifeng Han, Mengwu Huo, Deyuan Hu, Chaoxin Huang, Hengyuan Zhang, Sihao Deng, Lunhua He, Juan Rodriguez-Carvajal, Abhisek Bandyopadhyay, Alessandro Puri, Devashibhai Adroja, Xiang Chen, Tao Xie, Zhen Chen, Hualei Sun, Meng Wang
  • Affiliations: Institut Laue-Langevin, Chinese Academy of Sciences, University of Bologna, Hainan University, CNR - Istituto Officina dei Materiali, Sun Yat-Sen University, University of Chinese Academy of Sciences, Lalit Narayan Mithila University, ISIS Neutron and Muon Facility, University of Johannesburg, Spallation Neutron Source Science Center
  • Link: https://arxiv.org/abs/2605.04562
  • Paper page: Regulating oxygen content and superconductivity in La₃Ni₂O₇₊δ

Summary: In this study, a series of La3Ni2O7+δ polycrystalline samples with tunable oxygen content were synthesized by systematically controlling annealing conditions, and XAFS, neutron powder diffraction, synchrotron X-ray diffraction, STEM, and thermogravimetric analysis were combined to determine their oxygen stoichiometry and microstructure. The results show that oxygen content not only affects NiO6 octahedral distortion but also drives the microstructure to evolve from bilayer and monolayer–bilayer mixed phases to a pure bilayer phase, and further to bilayer-dominated samples containing trilayer intergrowth phases. High-pressure transport measurements revealed distinct superconducting transitions and markedly different Tc corresponding to the bilayer, mixed, and trilayer intergrowth phases; moreover, oxygen content directly modulates the upper critical field Hc2 of bilayer superconductivity. On this basis, the authors established a phase diagram of Tc and Hc2 as a function of oxygen content in La3Ni2O7+δ, thereby advancing synthetic control of this class of Ruddlesden–Popper nickelates and providing new clues for understanding their high-temperature superconductivity mechanism.

2. Origin of superconductivity in bilayer nickelates: a Quantum Monte Carlo study for a sign-problem-free effective model

Summary: This paper employs determinant quantum Monte Carlo to study a two-orbital model of the bilayer nickelate La3Ni2O7. With realistic dispersion and specific interaction parameters, the auxiliary-field-decoupled fermionic Hamiltonian possesses Kramers antiunitary symmetry and is therefore sign-problem-free. By tuning doping, interlayer tunneling, and Hund’s coupling, the authors find that the system can form spin-singlet layer-triplet superconductivity, whose transition temperature is affected by doping and Hund’s coupling; lower doping favors superconductivity, whereas excessive doping suppresses or even eliminates it. Interlayer tunneling plays a decisive role in the competition between superconductivity and (π,π) interlayer bond order: in the strong-interaction limit, the same symmetry also leads to a bond-order instability, which may be related to the mysterious density wave observed experimentally and is accompanied by spin-density-wave fluctuations near (π,π). The conclusion suggests that enhancing superconductivity can be achieved by strongly breaking particle-hole symmetry and weakening interlayer/subspace tunneling, the latter being consistent with the role of apical oxygen vacancies in stabilizing superconductivity.

3. Multiorbital Anisotropy and Magnetic Excitations in Trilayer Nickelate Pr$_4$Ni$_3$O$_{10}$

Summary: Here, combining X-ray absorption spectroscopy and resonant inelastic X-ray scattering, we investigate the multi-orbital electronic structure and magnetic excitations of the trilayer nickelate Pr4Ni3O10. Because the Pr resonances do not cover the Ni L3 edge, the Ni L3 edge can be probed directly; polarization-dependent measurements at the Ni L edge and O K edge resolve in-plane and out-of-plane Ni-O hybridization channels. Momentum-resolved RIXS reveals dispersive magnetic excitations that soften at the incommensurate spin-density-wave wavevector. Effective spin-wave analysis yields substantial intra-trilayer exchange coupling, comparable in magnitude to the dominant in-plane interaction and insensitive to rare-earth substitution. These results indicate that the multilayer structure, rather than rare-earth substitution alone, is the key factor tuning the magnetic interactions in this class of materials.