Daily Overview: Today’s highlight centers on a theoretical study of the superconducting mechanism in the 1313 phase La₃Ni₂O₇. Through combined DFT+DMFT and RPA analysis, it is revealed that the single-layer NiO₂ plane is nearly insulating and the d_{z²} orbital exhibits Mott physics, while superconductivity is predominantly confined to the metallic trilayer subsystem and forms s^±-wave pairing symmetry. The study points out that hole doping in the trilayer weakens Fermi surface nesting, and together with the extremely weak S–N–S Josephson junction formed by the nearly insulating monolayer, leads to its superconducting transition temperature being far lower than that of the bulk material. It further clarifies that the high-temperature superconductivity in this Ruddlesden-Popper series should be attributed to the 2222 phase rather than the 1313 phase. arXiv submission processing window: 2026-07-28 00:00 to 2026-07-28 00:00 UTC.

1. Pairing mechanism and superconductivity in 1313 phase La$_3$Ni$_2$O$_7$

Summary: This study employs density functional theory combined with dynamical mean-field theory (DFT+DMFT) and the random phase approximation (RPA) to systematically investigate the electronic structure and superconducting mechanism of the 1313 phase of La₃Ni₂O₇. DFT+DMFT calculations reveal that the monolayer subsystem is nearly insulating, with the d_z² orbital exhibiting Mott physics, while the trilayer subsystem remains metallic with its Ni-e_g orbitals being hole-doped relative to bulk La₄Ni₃O₁₀, and superconductivity is predominantly confined within the trilayer subsystem. Based on a low-energy Hamiltonian derived from DMFT, RPA analysis yields s^±-wave pairing symmetry within the trilayer subsystem. The study identifies two key factors that drastically lower the T_c of the 1313 phase compared to the bulk: first, hole doping in the trilayer subsystem weakens Fermi surface nesting, reducing the pairing strength; second, the nearly insulating monolayer subsystem acts as a weak link, coupling the superconducting trilayer subsystems into S-N-S Josephson junctions, and the extremely weak interlayer Josephson coupling suppresses global phase coherence, further depressing T_c. Consequently, the high-temperature superconducting phase of the Ruddlesden-Popper series La₃Ni₂O₇ is attributed to the 2222 phase rather than the 1313 phase.