Daily Overview: Today’s highlights focus on the multidimensional exploration of Ruddlesden-Popper-type nickelate superconductivity. An experimental study successfully prepared Pr$_3$Ni$_2$O$_7$ thin films through epitaxial stabilization and observed superconductivity under high pressure, with an onset transition temperature as high as 66 K. It was also found that the critical pressure required for superconductivity increases with decreasing rare-earth ion radius, providing a new pathway for expanding the bilayer nickelate superconductor family. On the other hand, theoretical calculations reveal that electron doping can universally enhance $s^\pm$-wave pairing superconductivity in La$_3$Ni$_2$O$_7$, and propose heterojunctions as a feasible experimental realization approach, where interorbital synergy is key to the instability of two-orbital cooperative superconductivity. Additionally, at the methodological level, a study combined DFT+U with the finite displacement method to systematically evaluate the impact of Hubbard corrections on electron-phonon interactions in the infinite-layer nickelate LaNiO$_2$, finding that the coupling strength is insufficient to explain the experimentally observed superconducting temperature, highlighting the critical roles of Fermi surface topology and correlation effects on electron-phonon coupling. arXiv submission processing window: 2026-05-21 00:00 to 2026-05-21 00:00 UTC.

1. Pressure-induced superconductivity in epitaxially-stabilized Pr$_3$Ni$_2$O$_7$ films

Summary: In this study, Pr3Ni2O7 thin films were successfully synthesized on LaAlO3 substrates via epitaxial stabilization, overcoming the thermodynamic stability limitations that hinder bulk synthesis of this compound. Under ambient pressure, the Pr3Ni2O7 films exhibited insulating behavior regardless of ozone annealing treatment; however, under a high pressure of 22 GPa, the films displayed T-linear metallic transport and superconductivity, with an onset superconducting transition temperature of 66 K and a zero-resistance temperature of approximately 40 K. Further investigation revealed that while Nd3Ni2O7 films incorporating the smaller rare-earth ion Nd could also be epitaxially stabilized, no superconductivity was observed within the measured pressure range. Comparison of La, Pr, and Nd Ln3Ni2O7 films showed that the critical pressure Pc required for superconductivity increases with decreasing Ln ionic radius, a trend consistent with Ln substitution studies in bulk materials. This work demonstrates that epitaxial stabilization is an effective approach for expanding the bilayer nickelate superconductor family, offering an important pathway for exploring novel superconducting materials.

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

Summary: Using first-principles calculations and large-scale dynamic cluster quantum Monte Carlo simulations, this work systematically investigates the effect of electron doping on the superconducting properties of two-orbital bilayer models for three representative systems: bulk La₃Ni₂O₇ under ambient pressure and at 15 GPa, as well as the La₃Ni₂O₇:La₃Al₂O₇ heterostructure. The results show that electron doping universally enhances s±-wave pairing superconductivity, with the heterostructure exhibiting the highest superconducting transition temperature in the underdoped region, even exceeding that of bulk samples under 15 GPa pressure. Further analysis reveals an inter-orbital synergistic mechanism: pairing on the d_{z²} orbital induces pairing on the d_{x²-y²} orbital, which gradually dominates at low temperatures, forming a two-orbital collaborative superconducting instability. This conclusion is validated by simulations with two different cluster sizes. This study provides a theoretical prediction for enhanced superconductivity in electron-doped Ruddlesden-Popper phase nickelates and proposes the heterostructure as a feasible experimental pathway, awaiting future experimental verification.

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

Summary: This paper combines density functional theory with the Hubbard U correction (DFT+U) and the finite displacement method to achieve a full Hubbard-corrected calculation of phonon spectra and electron-phonon matrices in strongly correlated materials. The authors apply this method to two representative systems: infinite-layer nickelate LaNiO₂ and ruthenium dioxide RuO₂. The results show that in 20% hole-doped LaNiO₂, the Hubbard U correction weakly enhances the electron-phonon interaction, but the total coupling strength remains small and insufficient to explain the experimentally observed superconducting transition temperature of approximately 10–30 K; this contradicts recent predictions from the GW correction, with the discrepancy arising from differences in the Fermi surface topology obtained by DFT+U and GW methods. In RuO₂, the Hubbard U correction eliminates imaginary phonon modes under TiO₂ substrate strain and significantly reduces the electron-phonon coupling, alleviating the contradiction between the theoretically overestimated electron-phonon coupling and the experimentally observed low superconducting transition temperature. This work provides a computational scheme that fully incorporates the Hubbard U correction for electron-phonon properties and highlights the critical influence of Fermi surface shape and correlation effects on phonon spectra and electron-phonon matrices.