Daily Overview: Today’s highlighted work focuses on a deeper understanding of the electronic structure of mixed Ruddlesden–Popper nickelates. Kong et al. combined ambient-pressure broadband infrared-to-visible reflectivity spectroscopy with high-temperature Raman measurements to track the electronic response of La₃Ni₂O₇ across the transition at about 544 K from the NiO₆ octahedral tilted phase to the untilted structure. They found a pronounced redistribution of spectral weight over an extremely broad energy range, with excitations shifting from 1–3 eV to low-energy excitations below 1 eV; moreover, the two low-energy interband excitations progressively approach and merge upon entering the untilted phase. Drude–Lorentz analysis further indicated that these changes arise mainly from finite-energy excitations rather than the Drude response, and point to a reconstruction of bilayer Ni 3d_{z²}-derived electronic states, whose interlayer coupling is considered central to the superconducting mechanism of La₃Ni₂O₇. The authors therefore propose that the untilted transition can directly reorganize the electronic degrees of freedom relevant to high-temperature superconductivity and provide an ambient-pressure reference for understanding the electronic structure of the superconducting state. arXiv submission processing window: 2026-10-01 00:00 to 2026-10-01 00:00 UTC.

1. Electronic Reconstruction across the Tilt-Free Transition in La$_3$Ni$_2$O$_7$

Summary: This work uses ambient-pressure broadband infrared-to-visible reflectivity spectra (15 meV–3.2 eV) combined with high-temperature Raman measurements to investigate the electronic response of La3Ni2O7 before and after its transition at approximately 544 K from a NiO6 octahedrally tilted phase to an untilted structure. The results show that spectral weight undergoes pronounced redistribution over an exceptionally broad energy range, transferring from 1–3 eV excitations to low-energy excitations below 1 eV; in particular, two low-energy interband excitations gradually approach and merge upon entering the untilted phase, indicating a substantial reconstruction of the finite-energy electronic structure. Drude–Lorentz analysis further attributes these changes mainly to finite-energy excitations rather than the Drude response, and points to reconstruction of bilayer Ni 3d_{z^2}-derived electronic states, whose interlayer coupling is considered central to the superconducting mechanism of La3Ni2O7. On this basis, the authors argue that the transition to the untilted phase can directly reorganize electronic degrees of freedom relevant to high-temperature superconductivity and provide an ambient-pressure reference for the electronic structure of the superconducting state.