Daily Overview: Today’s highlight work focuses on deepening the understanding of the electronic structure of mixed Ruddlesden-Popper nickelates. In [1], a theoretical study based on a bilayer two-orbital Hubbard model reveals how electron correlations drive orbital-selective Fermi surface reconstruction in La₃Ni₂O₇: the d_{z²} orbital spectral weight is depleted, the γ band sinks below the Fermi level, while the d_{x²-y²} orbital forms Fermi arcs. Concurrently, the superconducting pairing transitions from an interlayer spin singlet dominated by the d_{z²} orbital under weak coupling to a pairing dominated by the d_{x²-y²} orbital under strong coupling, while consistently maintaining s±-wave symmetry. This indicates that the disappearance of the γ Fermi surface does not suppress superconductivity but rather signifies a correlation-driven change in the pairing channel. In [2], through a systematic analysis of strained La₃Ni₂O₇ thin films, it is found that biaxial compressive strain predominantly elongates the outer apical Ni–O bonds, significantly enhancing the Jahn-Teller splitting while hardly affecting interlayer d_{z²} orbital hopping. This identifies Jahn-Teller distortion as a key microscopic parameter for strain-tuned electronic structure and supports its central role in optimizing superconductivity. arXiv submission processing window: 2026-05-12 00:00 to 2026-05-12 00:00 UTC.

1. Correlation-Driven Orbital-Selective Fermiology and Superconductivity in the Bilayer Nickelate La$_3$Ni$_2$O$_7$

Summary: Based on the bilayer two-orbital Hubbard model, this study systematically investigates the effects of electronic correlations on the Fermi surface topology and superconducting pairing symmetry in La₃Ni₂O₇ using the time-dependent variational principle cluster perturbation theory (TDVP-CPT) and large-scale density matrix renormalization group (DMRG) methods. TDVP-CPT calculations on clusters containing up to 16 physical sites reveal that electronic correlations drive significant orbital-selective low-energy spectral reconstruction: the spectral weight of the d_{z²} orbital is progressively depleted, the γ band sinks below the Fermi level, while the α and β bands exhibit a pseudogap, ultimately leading to the formation of a Fermi arc dominated by the d_{x²-y²} orbital in the strong-coupling regime. DMRG calculations further demonstrate that the dominant superconducting pairing correlations evolve consistently with this Fermi surface reconstruction, transitioning from interlayer spin singlet pairing mediated primarily by the d_{z²} orbital in the weak-coupling regime to pairing dominated by the d_{x²-y²} orbital in the strong-coupling regime, while maintaining s±-wave symmetry throughout. The study indicates that the disappearance of the γ Fermi surface does not suppress superconductivity but instead signifies a correlation-driven change in the pairing channel, with key intermediate mechanisms including interlayer antiferromagnetic fluctuations, Hund coupling, and interorbital hybridization.

2. Jahn-Teller distortion on strained La$_3$Ni$_2$O$_7$ thin films

Summary: This study systematically analyzes the electronic structure of strained La₃Ni₂O₇ thin films, revealing that biaxial compressive strain primarily elongates the outer apical Ni-O bonds while leaving the inner apical Ni-O bonds nearly unchanged. This asymmetric structural response leads to a significant enhancement of Jahn-Teller splitting ΔJT, yet the interlayer d_{z²} orbital hopping t⊥ᶻ varies only weakly. Given that superconductivity is generally observed only when the in-plane lattice constant falls below a critical value, strain-enhanced ΔJT is identified as a key microscopic tuning parameter. The calculated Fermi surfaces and Hall responses on LaAlO₃ and SrLaAlO₄ substrates are consistent with ARPES and Hall measurements. These results reveal that Jahn-Teller distortion dominates the electronic structure in strained La₃Ni₂O₇ films and support its central role in optimizing superconductivity in bilayer nickelates.