A groundbreaking advancement in the field of superconductivity has been achieved with the discovery of nearly 100 K superconductivity in bilayer nickelate single crystals synthesized at ambient pressure. This breakthrough challenges long-standing restrictions associated with high-pressure synthesis methods and opens new avenues for exploring high-temperature superconductivity beyond cuprates and iron-based superconductors. The recent study, led by Li, F., Xing, Z., Peng, D., and collaborators, reports superconductivity up to 96 K in La-substituted Sm nickelates under high-pressure conditions and provides unprecedented insights into the structural and electronic factors that stabilize the superconducting phase.
The resurgence of interest in nickelate superconductors has been fueled by the discovery of La3Ni2O7 exhibiting superconductivity around 80 K above 14 GPa. However, the quest for higher transition temperatures (Tc) and the preparation of single crystals without resorting to complex high oxygen-pressure growth has hindered progress. The novel approach used in this study bypasses these challenges by synthesizing bilayer La2SmNi2O7−δ single crystals via flux growth at ambient pressure, achieving remarkable homogeneity and crystallinity evident from extensive characterization methods. These techniques include energy-dispersive spectroscopy (EDS), single-crystal X-ray diffraction (XRD), nuclear quadrupole resonance (NQR), and scanning transmission electron microscopy (STEM), all confirming the impeccable quality of the as-grown crystals.
The measured superconducting properties of La2SmNi2O7−δ single crystals are among the most impressive for nickelates to date. Resistivity measurements under pressure reveal zero resistance indicative of bulk superconductivity, with the onset temperature (Tc,max onset) reaching 92 K and zero-resistance temperature (Tc,max zero) at 73 K around 21 GPa. Magnetic susceptibility experiments further underscore bulk superconductivity with a clear Meissner effect emerging at 60 K when subjected to 20.6 GPa. These results firmly establish the viability of high-pressure induced superconductivity in bilayer nickelates with an even wider superconducting window than previously observed in related compounds.
One of the most compelling outcomes of this study is the detailed structural analysis under low temperatures and high pressure, which uncovers that superconductivity can be hosted in both monoclinic and tetragonal crystallographic phases. This contrasts earlier reports that associated superconductivity primarily with one specific lattice symmetry, suggesting a more nuanced relationship between crystal structure and superconducting pairing mechanisms in nickelates. Such revelations challenge existing theoretical frameworks and invite fresh perspectives on the interplay between lattice distortions, electronic correlations, and superconductivity.
Another landmark finding concerns the correlation between lattice distortion at ambient pressure and the superconducting transition temperature under high pressure. The researchers demonstrate that a larger in-plane lattice distortion, tunable through partial La/Sm substitution (manifested in La1.57Sm1.43Ni2O7−δ), pushes the onset Tc to an unprecedented 96 K at comparable pressures. This correlation suggests that lattice strain engineering at ambient conditions can effectively optimize superconducting properties when external pressure is applied, providing a strategic roadmap for designing nickelate superconductors with enhanced Tc.
The synthesis of high-quality single crystals without the reliance on elevated oxygen pressures is a pivotal advancement that addresses a major bottleneck in the field. Traditional approaches to nickelate superconductors have faced reproducibility issues and complications due to oxygen stoichiometry control under extreme conditions. The flux growth method adopted here not only simplifies sample preparation but also enables more precise control over chemical composition and structural homogeneity, which are critical for reliable experimental investigations and potential applications.
Nuclear quadrupole resonance and scanning transmission electron microscopy have played crucial roles in verifying the intrinsic nature of superconductivity and the high crystalline order of the samples. NQR offers microscopic insights into the local electronic environments, confirming bulk superconductivity without impurity-driven artifacts. STEM imaging further reveals atomic-scale uniformity, bolstering confidence in the structural integrity and correlation between crystal lattice parameters and superconducting behavior.
The implications of these findings extend beyond nickelates, contributing to the broader understanding of unconventional superconductivity in correlated oxides. The coexistence of superconductivity with different structural motifs in La2SmNi2O7−δ offers valuable clues for exploring pairing mechanisms, particularly the interplay of electron correlation, lattice distortions, and multi-orbital physics. These insights may inspire new theoretical models and computational studies that better capture the complexity of high-temperature superconductivity.
Moreover, the observed pressure-induced enhancement of Tc approaching 100 K nudges nickelates closer to the realm traditionally dominated by cuprate superconductors, revitalizing interest in nickel oxides as a fertile platform for superconductivity research. The ability to engineer higher transition temperatures via chemical substitution and lattice manipulation underlines the tunability of this material class and sets the stage for further experimental and technological breakthroughs.
Future research directions will likely focus on extending the approach demonstrated here to other rare-earth-substituted nickelates and achieving superconductivity at ambient pressure through chemical or epitaxial strain engineering. This study paves the way toward practical applications by reducing complexity in sample synthesis and improving material stability and homogeneity, prerequisites for device integration and scalability.
In summary, the discovery of bulk superconductivity reaching 96 K in ambient-pressure grown bilayer nickelate single crystals represents a significant leap forward. The combination of sophisticated synthesis, multi-faceted characterization, and comprehensive structural analysis delivers a holistic understanding of the factors governing superconductivity in this emerging family of compounds. These findings hold promise for not only advancing fundamental condensed matter physics but also propelling nickelate superconductors closer to real-world applications in energy-efficient technologies.
Subject of Research: Bilayer nickelate superconductors synthesized at ambient pressure exhibiting bulk superconductivity at temperatures up to 96 K under high pressure.
Article Title: Bulk superconductivity up to 96 K in pressurized nickelate single crystals.
Article References:
Li, F., Xing, Z., Peng, D. et al. Bulk superconductivity up to 96 K in pressurized nickelate single crystals. Nature (2025). https://doi.org/10.1038/s41586-025-09954-4
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