Daily Overview: Today’s highlights focus on an in-depth understanding of the electronic structure of hybrid Ruddlesden–Popper nickelates. [1] Using polarization-resolved electronic Raman scattering in La₃Ni₂O₇ single crystals, a symmetry-dependent gap of the spin-density-wave transition around 150 K was observed, quantitatively yielding anisotropic SDW gaps of approximately 37.5–40.4 meV near the X/Y points and approximately 23.0 meV along the diagonal direction. This indicates that the SDW is driven by anisotropic electronic correlations and has unconventional character, providing a microscopic basis for understanding high-temperature superconductivity under pressure. [2] Combining first-principles calculations and large-scale dynamical cluster quantum Monte Carlo simulations, electron-doped La₃Ni₂O₇ systems were systematically studied. It was found that electron doping generally enhances s±-wave superconductivity and that Tc varies in a dome-like manner, with the La₃Ni₂O₇/La₃Al₂O₇ heterostructure exhibiting the highest Tc in the underdoped region. The study further reveals an interorbital synergy mechanism in which the d_{z²} orbital dominates interlayer s± pairing and induces pairing in the d_{x²-y²} orbital. In addition, [3] a Hubbard-U-corrected finite-displacement method was developed to calculate electron–phonon interactions in strongly correlated materials. Studies of hole-doped infinite-layer nickelate LaNiO₂ show that the U correction only slightly enhances electron–phonon coupling, which is still insufficient to explain its superconducting transition temperature of 10–30 K, and the discrepancy with full GW results is attributed to differences in Fermi surface topology. This method also provides a more self-consistent description of phonon and electron–phonon calculations for correlated nickelates and systems such as RuO₂. arXiv submission processing window: 2026-08-24 00:00 to 2026-08-24 00:00 UTC.

1. Anisotropic Electronic Correlations in the Spin Density Wave State of La$_3$Ni$_2$O$_7$

Summary: Using polarization-resolved electronic Raman scattering, we investigate the density-wave transition at about 150 K in single crystals of the bilayer nickelate La₃Ni₂O₇. Below 150 K, the B₁g and B₂g channels exhibit distinct symmetry-dependent spectral weight redistribution, consistent with the opening of a spin-density-wave (SDW) gap; the B₁g channel shows an asymmetric coherence peak, whereas the B₂g channel shows a broad and nearly symmetric peak. Quantitative analysis yields a momentum-selective SDW gap: near the X/Y points of the Brillouin zone the gap is about 37.5–40.4 meV, corresponding to 2Δ/k_BT ≈ 5.5–5.9 and indicating intermediate-to-strong coupling, whereas along the diagonal direction the gap is about 23.0 meV, corresponding to 2Δ/k_BT ≈ 3.4 and indicating weak coupling. These results suggest that the SDW in La₃Ni₂O₇ has unconventional character driven by anisotropic electronic correlations, provide a possible explanation for why angle-resolved photoemission spectroscopy (ARPES) has not observed a clear gap, and offer a microscopic basis for understanding the emergence of high-temperature superconductivity in nickelates under pressure.

2. Enhanced $s^\pm$-wave superconductivity in electron-doped La$_3$Ni$_2$O$_7$

Summary: Using first-principles calculations and large-scale dynamical cluster quantum Monte Carlo simulations, this work systematically investigates electron doping effects in three La₃Ni₂O₇ systems—ambient-pressure bulk, 15 GPa bulk, and La₃Ni₂O₇:La₃Al₂O₇ heterostructure—within a two-orbital bilayer model. It is found that electron doping generally enhances s±-wave pairing superconductivity in all three systems, with the superconducting transition temperature exhibiting a dome-shaped dependence on doping concentration; among them, the heterostructure shows the highest Tc in the underdoped region. Further analysis reveals that the d_{z²} orbital dominates interlayer s± pairing and induces pairing in the d_{x²-y²} orbital, forming an interorbital synergistic mechanism that plays a key role in the superconducting instability. This work provides theoretical predictions for enhanced superconductivity in electron-doped RP nickelates and calls for future experimental verification.

3. Hubbard-$U$-corrected electron-phonon interactions in strongly correlated materials via the finite-displacement method

Summary: This paper proposes combining DFT+U with the finite-displacement method to calculate the phonon spectra and electron-phonon g matrix of strongly correlated materials, so that the Hubbard U correction acts simultaneously on the electronic structure, phonons, and electron-phonon coupling. Studies of 20% hole-doped infinite-layer nickelate LaNiO₂ show that the Hubbard U correction only slightly enhances the electron-phonon coupling; the total coupling remains small and insufficient to explain a superconducting transition temperature of about 10–30 K. This contrasts with full GW results, where the coupling is about five times the DFT value, which the authors attribute to differences in Fermi surface topology between the two methods. For strained RuO₂ on a TiO₂ substrate, adding the Hubbard U correction removes its imaginary-frequency phonon modes, making the system dynamically stable, and significantly reduces the electron-phonon coupling, thereby alleviating the previous discrepancy between overestimated theoretical coupling and the low experimental superconducting transition temperature. Overall, this algorithm achieves a complete Hubbard U correction to the electron-phonon properties of correlated materials and highlights the important role of Fermi surface shape and correlation effects in the phonon spectra and electron-phonon g matrix.