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.

1. Weak coupling theory of nickel-based 327 superconductors

Summary: This review summarizes weak-coupling theoretical studies of superconductivity in pressurized bilayer nickelate La₃Ni₂O₇, primarily employing the random phase approximation (RPA), fluctuation exchange approximation (FLEX), and functional renormalization group (FRG), based on a bilayer two-orbital Hubbard model with Ni d_{x²-y²} and d_{3z²-r²} orbitals. Studies show that under pressure the Fermi surface consists of an electron-like α pocket and hole-like β and γ pockets; the γ pocket, dominated by the d_{3z²-r²} orbital, exhibits strong nesting with the other pockets, significantly enhancing antiferromagnetic spin fluctuations and mediating attractive pairing. Different methods generally predict the dominant pairing symmetry to be s±-wave: the superconducting gaps on the γ and α pockets have the same sign, whereas the β pocket has the opposite sign, and this pairing is closely related to the interlayer pairing channel dominated by the d_{3z²-r²} orbital. RPA efficiently describes spin and charge susceptibilities, FLEX self-consistently renormalizes quasiparticles and spin fluctuations, and FRG can treat competing orders such as superconductivity, spin density wave, and charge density wave in an unbiased manner. The review concludes that weak-coupling theory can effectively connect Fermi surface geometry with the spin-fluctuation pairing mechanism, and points out that future studies should be combined with strong-coupling pictures and more accurate first-principles parameters.