Bulk high-temperature superconductivity in pressurized tetragonal La₂PrNi₂O₇

摘要

The Ruddlesden–Popper (R–P) bilayer nickelate, La₃Ni₂O₇, was recently found to show signatures of high-temperature superconductivity (HTSC) at pressures above 14 GPa (ref. 1). Subsequent investigations achieved zero resistance in single-crystalline and polycrystalline samples under hydrostatic pressure conditions2–4. Yet, obvious diamagnetic signals, the other hallmark of superconductors, are still lacking owing to the filamentary nature with low superconducting volume fraction2,4,5. The presence of a new 1313 polymorph and competing R–P phases obscured proper identification of the phase for HTSC₆–9. Thus, achieving bulk HTSC and identifying the phase at play are the most prominent tasks. Here we address these issues in the praseodymium (Pr)-doped La₂PrNi₂O₇ polycrystalline samples. We find that substitutions of Pr for La effectively inhibit the intergrowth of different R–P phases, resulting in a nearly pure bilayer structure. For La₂PrNi₂O₇, pressure-induced orthorhombic to tetragonal structural transition takes place at Pc ≈ 11 GPa, above which HTSC emerges gradually on further compression. The superconducting transition temperatures at 18–20 GPa reach T_rmc^rmonset=82.5 rmKand T_rmc^rmzero=60 rmK, which are the highest values, to our knowledge, among known nickelate superconductors. Importantly, bulk HTSC was testified by detecting clear diamagnetic signals below about 75 K with appreciable superconducting shielding volume fractions at a pressure of above 15 GPa. Our results not only resolve the existing controversies but also provide directions for exploring bulk HTSC in the bilayer nickelates.

材料

• La₂PrNi₂O₇ polycrystalline

方法

• Pr substitution
• High-pressure measurements
• X-ray diffraction
• Magnetic susceptibility measurements

关键词

• bulk superconductivity
• diamagnetic signals
• superconducting volume fraction
• orthorhombic to tetragonal transition

亮点

• Achieves bulk high-temperature superconductivity in bilayer nickelates.
• Resolves existing controversies about the phase responsible for HTSC.

结论

• Pr substitution inhibits intergrowth of different R–P phases, resulting in nearly pure bilayer structure.
• Bulk HTSC with T_c onset 82.5 K and zero 60 K at 18–20 GPa with clear diamagnetic signals.

主要论断

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研究流程

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