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Researchers have developed a technique to integrate free-standing infinite-layer Nd₀.₈₅Sr₀.₁₅NiO₂ thin films into diamond anvil cells, thereby overcoming the difficulties of measuring such films under high-pressure conditions. By applying pressures up to approximately 90 GPa to the films, they observed that the superconducting transition temperature (T_c) increased monotonically and linearly from about 17 K at ambient pressure to roughly 74.2 K, with an enhancement rate of approximately 0.65 K/GPa and no signs of saturation. This linear, non-saturating pressure dependence of T_c markedly differs from the pressure-induced overdoping that leads to T_c suppression in most copper oxide superconductors and bilayer nickelates, suggesting that the pairing strength in infinite-layer nickelates can be elevated to unexpectedly high levels. Furthermore, measurements of the upper critical field and coherence length confirm the pressure-induced enhancement of the superconducting state. This study provides a new pathway for continuously enhancing superconductivity through lattice compression, and the developed free-film high-pressure technique holds promise for broad application to other two-dimensional materials.

Recent experimental observations have showed some signatures of superconductivity close to 80 K in La3Ni2O7 under pressure and have raised the hope of achieving high-temperature superconductivity in bulk nickelates. However, a zero-resistance state—a key characteristic of a superconductor—was not observed. Here we show that the zero-resistance state does exist in single crystals of La3Ni2O7−δ using a liquid pressure medium at up to 30 GPa. We also find that the system remains metallic under applied pressures, suggesting the absence of a metal–insulator transition proximate to the superconductivity. Moreover, analysis of the normal state T-linear resistance reveals a link between this strange-metal behaviour and superconductivity. The association between strange-metal behaviour and high-temperature superconductivity is very much in line with other classes of unconventional superconductors, including the cuprates and Fe-based superconductors. Further investigations exploring the interplay of strange-metal behaviour and superconductivity, as well as possible competing electronic or structural phases, are essential to understand the mechanism of superconductivity in this system.

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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.

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Identification of superconductivity in the Ruddlesden-Popper phases of nickelates under high pressure remains challenging. Here, we report a comprehensive study of the crystal structure, electrical resistance, and Meissner effect in single crystals of bilayer nickelate La3Ni2O7 under hydrostatic pressures up to 104 GPa. Using high-pressure X-ray diffraction, we observe a structural transition from an orthorhombic to a tetragonal phase above 40 GPa. Superconductivity emerges with a maximum onset transition temperature Tconset of 83 K at 18.0 GPa, accompanied by zero resistance. The superconducting phase is gradually suppressed and vanishes above 80 GPa, forming a right-triangle-like superconducting region. Direct-current magnetic susceptibility measurements demonstrate the Meissner effect and reveal a superconducting volume fraction of ∼41% at 22.0 GPa and 20 K, confirming the bulk nature of superconductivity in La3Ni2O7. Our results highlight the intricate relationship between superconductivity, oxygen content, and structural transitions in this material.