Daily Overview: Today’s highlighted work focuses on the microscopic theoretical elucidation of the magnetic ground state of the bilayer Ruddlesden–Popper nickelate La₃Ni₂O₇. Based on an orbital-selective Mott physics picture, the study describes the system as consisting of itinerant d_{x²−y²} quasiparticles coexisting with localized d_{z²} magnetic moments, and by integrating superexchange and RKKY interactions, reveals a magnetic frustration mechanism dominated by long-range coupling mediated by itinerant electrons. Theoretical calculations naturally yield a non-coplanar antiferromagnetic ground state consistent with neutron scattering experiments; the softening of the spin-wave spectrum at the ordering wave vector and the total bandwidth of about 80 meV are also consistent with resonant inelastic X-ray scattering data, indicating that orbital-selective correlations are the core factor determining the magnetism of bilayer nickelates and suggesting that low-energy magnetic fluctuations may provide the driving force for unconventional superconducting pairing. arXiv submission processing window: 2026-07-17 00:00 to 2026-07-17 00:00 UTC.

1. Magnetic Order in bilayer Ruddlesden-Popper Nickelates

Summary: Based on experimental evidence of orbital-selective electronic correlations, this work proposes a new magnetic description framework for bilayer nickelate La₃Ni₂O₇. In the bad-metal regime of the normal state, the system lies close to an orbital-selective Mott phase, with the electronic spectrum decomposing into coherent d_(x²-y²) quasiparticles and incoherent d_(z²) local moments. An effective spin model incorporating superexchange between local moments and RKKY interactions mediated by coherent electrons is constructed, where the RKKY contribution dominates third-neighbor coupling and introduces magnetic frustration. The model naturally stabilizes a noncoplanar antiferromagnetic ground state with a wavevector near (π/2, π/2) and antiferromagnetic interlayer stacking, consistent with neutron scattering experiments. The calculated spin-wave spectrum contains low-frequency acoustic and high-frequency optical branches, with the acoustic branch softening at the ordering wavevector and an overall bandwidth of about 80 meV, in agreement with resonant inelastic X-ray scattering data. These results reveal that orbital-selective correlations are the essential ingredient determining magnetism in bilayer nickelates and indicate that low-energy magnetic fluctuations and short-range exchange interactions may provide the pairing glue for unconventional superconductivity.