Daily Overview: Today’s highlighted work focuses on deepening the understanding of the electronic structure of mixed Ruddlesden-Popper nickelates. In [1], a theoretical study based on first-principles and fluctuation exchange approximation (FLEX) systematically analyzed the crystal structure, electronic structure, and superconducting pairing properties of La₃Ni₂O₇ thin films on different substrates (LSAT, LAO, SLAO). By constructing a two-orbital bilayer Hubbard model with the inclusion of +U corrections, it was found that although the electronic structure (e.g., the presence or absence of the γ-pocket) depends on the crystal structure and computational details, the s±-wave pairing symmetry remains robust, and this robustness originates from pairing mediated by finite-energy spin fluctuations, which is insensitive to the Fermi surface topology. However, the observation that the superconducting transition temperature of the thin films (~40 K) is halved compared to that of the pressurized bulk (~80 K) can only be explained by models employing a small interlayer hopping integral (|t⊥|) derived from the experimental crystal structure, revealing the critical influence of lattice structure on Tc. This work provides an important theoretical perspective for understanding the relationship between structure and superconductivity in nickel-based superconducting thin films. arXiv submission processing window: 2026-05-27 00:00 to 2026-05-27 00:00 UTC.

1. Theoretical study on ambient pressure superconductivity in La$_3$Ni$_2$O$_7$ thin films : structural analysis, model construction, and robustness of $s\pm$-wave pairing

Summary: This study systematically analyzes the crystal structure, electronic structure, and superconducting pairing properties of La₃Ni₂O₇ thin films on different substrates (LSAT, LAO, SLAO) using first-principles structural optimization and the fluctuation exchange approximation (FLEX) method. By constructing a two-orbital bilayer Hubbard model corresponding to theoretically optimized and experimentally determined crystal structures, and incorporating the +U correction, it is found that while the electronic structure (e.g., the presence or absence of the γ-pocket) varies with crystal structure and computational details, the s±-wave pairing symmetry remains robust. This robustness is attributed to finite-energy spin fluctuation-mediated pairing, which is insensitive to the Fermi surface topology and yields a nearly momentum-independent interlayer d₃z²-r² pairing gap in the orbital representation. However, the observed reduction in the superconducting transition temperature of the thin film (approximately 40 K) compared to that of the pressurized bulk (approximately 80 K) can only be explained within the model derived from the experimentally determined crystal structure, which yields a small interlayer hopping integral (|t⊥|), indicating the crucial influence of lattice structure on Tc. The study notes that while the small |t⊥| model within the FLEX method can account for the Tc reduction, the possibility of other microscopic mechanisms cannot be ruled out.