Daily Overview: Today’s highlighted work focuses on a deeper understanding of the electronic structure of the mixed Ruddlesden–Popper nickelate. Using site-selective 17O NMR to investigate the spin-density-wave order in the bilayer nickelate La3Ni2O7, this work finds that below T_SDW = 150 K the planar O(3,4) sites are significantly broadened by internal magnetic fields, whereas the outer apical O(2) sites exhibit almost no internal field, consistent with a single-spin–no-spin stripe-type SDW picture. The internal field at the O(1) sites bridging the NiO2 layers is nearly canceled, indicating an antiparallel spin configuration between adjacent planes. However, below T_A ≈ 115 K the O(1) spectrum disappears, revealing that the antiparallel spin arrangement through the Ni–O(1)–Ni bonds is unstable, while the extremely small local spin susceptibility at the O(2) sites indicates that the Ni-d_{3z^2-r^2} orbitals have already formed well-developed interlayer spin singlets. These results highlight the orbital-selective nature of the coexistence of spin-density-wave order and interlayer spin singlets in this nickelate superconductor candidate, providing important insights for understanding its high-pressure superconducting mechanism. arXiv submission processing window: 2026-08-31 00:00 to 2026-08-31 00:00 UTC.

1. Orbital-Selective Coexistence of Interlayer Spin-Singlet Formation and SDW Order with Anomalous Spin Reconfiguration in Bilayer Nickelate La$_{3}$Ni$_{2}$O$_{7}$ Revealed by $^{17}$O-NMR

Summary: Site-selective (^{17})O-NMR measurements of the inner apical O(1), outer apical O(2), and planar O(3,4) sites were used to investigate the spin density wave order in the bilayer nickelate La(3)Ni(2)O(7). Below (T{\rm SDW}=150) K, all planar O(3,4) sites broaden significantly due to the appearance of internal magnetic fields, while the O(2) sites show almost no internal field, consistent with coherent spin density wave order with single-spin–no-spin (or large–small spin) stripes; the internal field at the O(1) sites bridging the NiO(2) planes nearly cancels, indicating an antiparallel spin configuration between adjacent planes. Below (T{\rm A}\sim 115) K, however, although the in-plane spin density wave order remains robust, the O(1) spectrum disappears, indicating that the antiparallel spin arrangement through the Ni–O(1)–Ni bonds is not particularly stable. In particular, the O(2) sites, which are strongly covalently bonded to the (d{3z^2-r^2}) orbitals, exhibit extremely small local spin susceptibility, suggesting that the Ni-(d{3z^2-r^2}) orbitals bridging the NiO(_2) planes already form a well-developed interlayer spin singlet. These results reveal interlayer spin singlet formation and an anomalous spin reconstruction through the Ni–O(1)–Ni bonding orbitals, reflecting the orbital-selective nature of this bilayer nickelate.