Daily Overview: Today’s highlighted work focuses on a deeper understanding of the electronic structure of mixed-type Ruddlesden-Popper nickelates. Motivated by pressure- or compressive-strain-induced high-temperature superconductivity in the bilayer nickelate La3Ni2O7, a study based on an effective four-orbital model, building on the fact that the normal-state electronic structure can give rise to bonding-antibonding s±-wave or d-wave pairing, further examined the orbital-antiphase sign structure of the superconducting gap. The authors first generalized the gap-node conditions of the single-layer two-orbital model to the bilayer system and, using the bonding/antibonding basis, related the nodal features to the signs and relative magnitudes of the intra- and interlayer pairing components. The results show that when the gaps on the pairing orbitals have opposite signs, additional node pairs appear on the α and/or β Fermi surface sheets in addition to the symmetry-enforced nodes; these nodes are not required by the symmetry of the gap function and can be detected by ARPES. Meanwhile, the orbital-antiphase gap also alters the temperature dependence of the low-temperature superfluid stiffness, providing concrete experimental criteria for testing this superconducting state in bilayer nickelates and related multiorbital systems. arXiv submission processing window: 2026-09-25 00:00 to 2026-09-25 00:00 UTC.

1. Nodal Orbital-Anti-Phase Superconducting State in Bilayer Nickelates

Summary: This paper investigates the orbital-antiphase structure of the superconducting gap in high-temperature superconductivity in the bilayer nickelate La3Ni2O7 induced by pressure or compressive strain, building on the notion that the normal-state electronic structure can give rise to bonding–antibonding s±-wave or d-wave pairing. Using an effective four-orbital model, the authors first analyze the gap-node conditions in a single-layer two-orbital model, then extend the analysis to the bilayer system, and employ the bonding/antibonding basis to relate the nodal characteristics to the signs and relative magnitudes of the intralayer and interlayer pairing components. The results show that when the gap changes sign between the orbitals involved in pairing, additional node pairs appear on the α and/or β Fermi surface sheets in addition to symmetry-enforced nodes; these nodes are not required by the symmetry of the gap function and can be detected by ARPES. Moreover, the orbital-antiphase gap modifies the temperature dependence of the low-temperature superfluid stiffness, providing concrete experimental criteria for testing this superconducting state in bilayer nickelates and related multiorbital systems.