Daily Overview: Today’s highlights focus on an in-depth understanding of the superconducting state and transport properties of bilayer Ruddlesden-Popper nickelates. In [1], Meng Zhang and Xi Yan systematically review the experimental progress of bilayer nickelate superconducting thin films under ambient pressure, pointing out that the reproducibility of pure-phase films, the microscopic origin of the two-step superconducting transition, the effects of oxygen defects and substrate doping, and the position of the Ni 3d({z^2})-derived γ band remain unresolved core issues. They call for establishing a more quantitative correlation among crystal structure, orbital reconstruction, and superconductivity. In [2], Seiichiro Onari et al., using a multi-orbital tight-binding model, reveal the crucial role of quasi-quantum metric terms in the temperature dependence of the Hall coefficient. This effect originates from orbital-selective renormalization induced by spin fluctuations in the Ni d({z^2}) orbital, successfully explaining the experimentally observed T-linear resistivity and the increase of the Hall coefficient with decreasing temperature. This provides a unified theoretical framework for understanding non-Fermi liquid transport in bilayer nickelates. arXiv submission processing window: 2026-05-13 00:00 to 2026-05-13 00:00 UTC.

1. Experimental Progress in Ambient-Pressure Superconducting Bilayer Nickelate Films

Summary: Bilayer Ruddlesden-Popper nickelates exhibit superconductivity near 80 K under high pressure, and recent work has stabilized RA₃Ni₂O₇ (RA = rare earth or alkaline earth element) superconducting thin films at ambient pressure via epitaxial strain, enabling transport, spectroscopic, microscopic, and device measurements. This review summarizes experimental progress on ambient-pressure superconducting bilayer nickelate thin films, covering synthesis routes, oxygen stoichiometry, substrate-induced strain, normal-state transport, superconducting properties, doping phase diagrams, and momentum-resolved electronic structure. Key unresolved issues include the reproducibility of phase-pure ultrathin films, the microscopic origin of the two-step superconducting transition, the roles of oxygen defects and substrate doping, the position of the Ni 3dz₂-derived γ band, and the pairing symmetry. The review concludes that future work must establish more quantitative links between crystal structure, orbital reconstruction, and superconductivity to deepen the understanding of this unconventional high-temperature superconducting system.

2. Impact of multiband effects on non-Fermi-liquid transport phenomena in bilayer nickelates

Summary: This study employs a multi-orbital tight-binding model to analyze non-Fermi liquid transport phenomena in the bilayer nickelate La₃Ni₂O₇, focusing on the influence of multiband effects on the Hall coefficient. Using the Green’s function method, a rigorous formula for the Hall coefficient incorporating the quasi-quantum metric (qQM) term is derived, revealing that the temperature dependence of this qQM term is crucial in strongly correlated multiband systems. Calculations show that spin fluctuations in the Ni d₂² orbital lead to stronger quasiparticle damping, while the Ni dₓ²₋ᵧ² orbital forms cold spots. The pronounced temperature dependence of the Hall coefficient in La₃Ni₂O₇ originates from the competition between the positive contribution of the hole band and the negative contribution of the electron band, with the qQM term enhancing the positive Hall coefficient at low temperatures and explaining the experimentally observed T-linear resistivity and the increase of the Hall coefficient upon cooling. Furthermore, the qQM term also plays a key role in describing the Nernst coefficient and other transport phenomena involving second derivatives of velocity. This study reveals the core mechanism of spin-fluctuation-induced orbital-selective renormalization in non-Fermi liquid transport, providing a theoretical framework for understanding the anomalous transport properties of this system.