Paper

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. ...

arXiv Daily: nickelate superconductors 2026-08-31

Daily Overview: Today’s highlight focuses on an in-depth understanding of the electronic structure of hybrid Ruddlesden–Popper nickelates. Through first-principles calculations, Song et al. identified a bipartite electronic structure in the bilayer nickelate La₃Ni₂O₅F, in which a Ni dpσ hole-type Fermi surface coexists with the cylindrical Fermi surface of an interstitial electron-type E* band. In this structure, self-doping by the interstitial states gives an effective Ni valence of about +1.09 and creates nearly nonanalytic Dirac points near the M point, which can be tuned by pressure or further fluorine insertion. The work further reveals that the interstitial density induces an even–odd splitting of approximately 1 eV in the Ni d_{z²} orbital. This two-fluid behavior, characterized by coexisting hole-type dpσ quasiparticles and interstitial electron-type quasiparticles, will significantly affect normal-state transport and far-infrared properties and may promote unconventional superconductivity. arXiv submission processing window: 2026-08-28 00:00 to 2026-08-28 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-08-28

Daily Overview: Today’s highlight focuses on a weak-coupling theoretical review of superconductivity in the pressurized bilayer nickelate La₃Ni₂O₇. This work systematically compares results from the random phase approximation (RPA), the fluctuation exchange approximation (FLEX), and the functional renormalization group (FRG) within a bilayer two-orbital Hubbard model. It indicates that under pressure the Fermi surface consists of an electron-type α pocket and hole-type β and γ pockets, and that the strong nesting between the d_{3z²-r²}-dominated γ pocket and the other pockets significantly enhances antiferromagnetic spin fluctuations and mediates attractive pairing. Different methods generally yield s±-wave pairing symmetry: the gaps on the γ and α pockets have the same sign, whereas the gap on the β pocket has the opposite sign, highlighting the crucial role of the d_{3z²-r²} interlayer pairing channel. The review argues that this weak-coupling picture effectively links Fermi surface geometry with the spin-fluctuation pairing mechanism, while noting that future work should combine it with strong-coupling descriptions and more accurate first-principles parameters. arXiv submission processing window: 2026-08-25 00:00 to 2026-08-25 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-08-25

Daily Overview: Today’s highlights focus on an in-depth understanding of the electronic structure of hybrid Ruddlesden–Popper nickelates. [1] Using polarization-resolved electronic Raman scattering in La₃Ni₂O₇ single crystals, a symmetry-dependent gap of the spin-density-wave transition around 150 K was observed, quantitatively yielding anisotropic SDW gaps of approximately 37.5–40.4 meV near the X/Y points and approximately 23.0 meV along the diagonal direction. This indicates that the SDW is driven by anisotropic electronic correlations and has unconventional character, providing a microscopic basis for understanding high-temperature superconductivity under pressure. [2] Combining first-principles calculations and large-scale dynamical cluster quantum Monte Carlo simulations, electron-doped La₃Ni₂O₇ systems were systematically studied. It was found that electron doping generally enhances s±-wave superconductivity and that Tc varies in a dome-like manner, with the La₃Ni₂O₇/La₃Al₂O₇ heterostructure exhibiting the highest Tc in the underdoped region. The study further reveals an interorbital synergy mechanism in which the d_{z²} orbital dominates interlayer s± pairing and induces pairing in the d_{x²-y²} orbital. In addition, [3] a Hubbard-U-corrected finite-displacement method was developed to calculate electron–phonon interactions in strongly correlated materials. Studies of hole-doped infinite-layer nickelate LaNiO₂ show that the U correction only slightly enhances electron–phonon coupling, which is still insufficient to explain its superconducting transition temperature of 10–30 K, and the discrepancy with full GW results is attributed to differences in Fermi surface topology. This method also provides a more self-consistent description of phonon and electron–phonon calculations for correlated nickelates and systems such as RuO₂. arXiv submission processing window: 2026-08-24 00:00 to 2026-08-24 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-08-24

Daily Overview: Today’s highlighted studies focus on the relationship between pressure, lattice, superconductivity, and magnetic order in bilayer Ruddlesden-Popper nickelates. A hydrostatic-pressure electronic Raman scattering study of La₃Ni₂O₇ single crystals shows that, with increasing pressure, the spin-density-wave (SDW) gap and transition temperature generally increase, while the dimensionless coupling ratio remains stable at about 7.5, indicating that the SDW state has strong-coupling character; however, the broadening of the SDW peak indicates that its long-range coherence is weakened, providing spectroscopic constraints for understanding the magnetic correlations associated with high-temperature superconductivity in bilayer nickelates. Another study of compressively strained La₂LnNi₂O₇ thin films finds that the superconducting transition temperature is approximately 41–42 K at ambient pressure and can be increased to 67–73 K under a high pressure of 16 GPa, whereas lattice compression induced by lanthanide substitution instead lowers Tc. Moreover, the variation of Tc correlates with the evolution of normal-state transport between T² and T-linear behavior, revealing the important influence of lattice structural changes on superconductivity in bilayer nickelates. arXiv submission processing window: 2026-08-19 00:00 to 2026-08-19 00:00 UTC. ...

arXiv Daily: nickelate superconductors 2026-08-19