Daily Overview: Today’s highlighted work focuses on a multi-perspective exploration of the superconductivity mechanism and phase diagram evolution in Ruddlesden-Popper phase bilayer nickelates. In [1], a review systematically summarizes the breakthrough progress in achieving ambient-pressure superconductivity in La₃Ni₂O₇ thin films, emphasizing the stabilization of the superconducting phase through epitaxial compressive strain and the controversial ARPES results regarding Fermi surface topology. It points out that weak-coupling theory predicts possible s± or d-wave pairing, but key issues remain unresolved. [2], from a theoretical perspective, proposes an orbital-space bilayer model (OSBM) and predicts that hole-doped reduced La₃Ni₂O₆ may be a new type of superconductor, with a pairing mechanism fundamentally different from that of La₃Ni₂O₇—driven by inter-orbital interactions in the incipient-band scenario, leading to s±-wave superconductivity, thereby opening a new theoretical direction for the nickelate superconductor family. [3] experimentally reveals the universal existence of a superconducting dome in compressively strained bilayer nickelate thin films. Through fine control of oxygen stoichiometry, it is found that strong scattering introduced by oxygen vacancies leads to a granular superconductor-insulator transition without changing the superconducting onset temperature, while interstitial oxygen mainly affects the carrier concentration. This phase diagram feature consistently appears across different rare-earth combinations and alkaline-earth-doped samples, providing key experimental evidence for understanding the relationship between electronic inhomogeneity and the emergence of superconductivity. arXiv submission processing window: 2026-03-13 00:00 to 2026-03-13 00:00 UTC.

1. Progress of ambient-pressure superconductivity in bilayer nickelate thin films

Summary: This review summarizes recent progress in achieving ambient-pressure superconductivity in bilayer nickelate La₃Ni₂O₇ thin films. Through epitaxial strain engineering, compressive strain provided by substrates such as SrLaAlO₄ successfully stabilizes the superconducting phase under ambient conditions, marking a significant breakthrough compared to the high-pressure superconductivity observed in bulk materials. In terms of experimental characterization, angle-resolved photoemission spectroscopy (ARPES) measurements reveal a controversially debated Fermi surface topology, with observations differing among research groups, likely due to variations in thin-film growth conditions. Regarding the enhancement of superconducting transition temperature (Tc), increasing compressive strain and optimizing growth techniques, such as giant oxide atomic layer epitaxy, enable Tc to reach approximately 60 K. Theoretical studies focus on electronic structures and pairing symmetries; weak-coupling approaches, including random phase approximation and functional renormalization group, predict s±-wave or d-wave pairing, while renormalized mean-field theory suggests the possibility of nodal d-wave pairing. However, key issues such as the specific role of electron pockets on the Fermi surface in superconductivity and the relationship between lattice ratio and Tc remain incompletely elucidated. These advances demonstrate that bilayer nickelate thin films serve as a highly tunable and exceptionally promising platform for studying high-temperature superconductivity.

2. Theoretical proposal of superconductivity in hole-doped reduced bilayer nickelate La3Ni2O6: a manifestation of orbital-space bilayer model with incipient bands

Summary: This study establishes a correspondence between the multi-orbital Hubbard model and the bilayer Hubbard model, proposing an orbital-space bilayer model (OSBM) in which the orbital energy level difference ΔE plays a role analogous to interlayer hopping in a real-space bilayer model, and superconductivity is enhanced in the incipient-band regime. Based on this, the theory predicts that the reduced bilayer nickelate La₃Ni₂O₆, under appropriate hole doping, can serve as a candidate OSBM superconductor. A tight-binding model constructed from first principles reveals a large ΔE between the Ni d_{x²-y²} orbital and other d orbitals due to the absence of apical oxygen atoms. Using the fluctuation-exchange approximation, calculations show that in the incipient-band scenario, intersite interactions can drive s±-wave superconductivity, where the superconducting gap function changes sign between the d_{x²-y²} band and other d-orbital bands. The study also examines the energetic and dynamic stability of the crystal structure under atomic substitution and pressure. Although La₃Ni₂O₇ and La₃Ni₂O₆ share similar chemical formulas, this work suggests that the latter may realize a completely different pairing mechanism.

3. A superconducting half-dome in bilayer nickelates

  • Relevance Score: 5.4253
  • Authors: Yidi Liu, Bai Yang Wang, Jiarui Li, Yaoju Tarn, Lopa Bhatt, Michael Colletta, Yi-Ming Wu, Cheng-Tai Kuo, Jun-Sik Lee, Berit H. Goodge, David A. Muller, Zhi-Xun Shen, Srinivas Raghu, Harold Y. Hwang, Yijun Yu
  • Affiliations: Cornell University, Stanford University, Max Planck Institute for Chemical Physics of Solids, SLAC National Accelerator Laboratory, Fudan University
  • Link: https://arxiv.org/abs/2603.12196
  • Paper page: A superconducting half-dome in bilayer nickelates

Summary: In compressively strained bilayer nickelate thin films, by continuously tuning the oxygen stoichiometry, researchers have discovered a superconducting half-dome. Starting from the optimal superconducting state, increasing the oxygen content progressively suppresses superconductivity, driving a transition toward a metallic phase; conversely, decreasing the oxygen content induces a granular superconductor-insulator transition while the onset superconducting temperature remains unchanged. This half-dome structure originates from the distinct roles of interstitial oxygen and oxygen vacancies: the former primarily regulates carrier concentration through doping effects, whereas the latter introduces strong scattering that leads to electronic inhomogeneity. Experiments show that this half-dome consistently appears across different rare-earth combinations and with or without alkaline-earth doping, revealing a universal feature of the bilayer nickelate phase diagram. This finding offers new perspectives for understanding the emergence and suppression of superconductivity in correlated electron systems.