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该研究通过将无限层钐镍氧化物超导薄膜制备成空间周期性网络结构，调控库珀对的相位相干性，实现了超导-绝缘体相变。实验中观测到周期为h/2e的磁阻振荡，直接证明了镍氧化物中2e库珀对的存在。相变主要受增强的超导涨落驱动，且库珀对在整个相变过程中参与电荷输运。研究还发现了两种异常金属态：一种出现在有限磁场下，另一种在零磁场下即可出现；这两种态均可由玻色子激发表征，暗示涡旋在基态中的动态角色。该工作确立了镍氧化物作为研究库珀对相位相干性调控下丰富玻色子相的关键平台。

Bosonic Phases across the Superconductor-Insulator Transitions in Infinite-Layer Samarium Nickelate

该研究系统研究了压应变La₂LnNi₂O₇薄膜（Ln为镧系元素）在常压与高压下的超导性，以揭示常压与高压超导机制之间的关系。通过59 T磁场抑制超导态，常压正常态电阻率趋于T²行为；在立方砧腔中施加高压后，Tc从常压的41–42 K提升至16 GPa时的67–73 K。然而，通过Ln替代引起的晶格压缩虽可能模拟压力效应，却使Tc降低。在上述两种情况下，Tc均与正常态输运在T²和T线性行为之间的演化相关，表明双层镍酸盐中晶格结构变化对超导性具有重要影响，为理解常压应变薄膜与高压体材料超导态的内在联系提供了线索。

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 $${T}_{{\rm{c}}}^{{\rm{onset}}}=82.5\,{\rm{K}}$$and $${T}_{{\rm{c}}}^{{\rm{zero}}}=60\,{\rm{K}}$$, 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.

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Recently, the Ruddlesden–Popper bilayer nickelate La3Ni2O7 has emerged as a superconductor with a transition temperature (Tc) of approximately 80 K above 14 GPa (refs. 1–3). Achieving a higher Tc in nickelate superconductors, along with the synthesis of reproducible high-quality single crystals without relying on high-oxygen-pressure growth conditions, remains a significant challenge4–7. Here we report superconductivity up to 96 K under high pressure in bilayer nickelate single crystals synthesized at ambient pressure. Energy-dispersive spectroscopy, single-crystal X-ray diffraction, nuclear quadrupole resonance and scanning transmission electron microscopy evidenced high crystal quality of the flux-grown La2SmNi2O7−δ single crystals. La2SmNi2O7 exhibits clear bulk superconductivity, including zero resistivity ( $${T}_{{\rm{c}},\max }^{{\rm{onset}}}$$ = 92 K and $${T}_{{\rm{c}},\max }^{{\rm{zero}}}$$ = 73 K at 21.6 GPa) and the Meissner effect (Tc = 60 K at 20.6 GPa). A low-temperature high-pressure structural study indicates that both monoclinic and tetragonal structures can support superconductivity in this bilayer nickelate. Furthermore, we established a correlation between higher Tc under high pressures and larger in-plane lattice distortion under ambient conditions, corroborated by observing even higher $${T}_{{\rm{c}}}^{{\rm{onset}}}$$of 96 K in La1.57Sm1.43Ni2O7−δ. This study overcomes key limitations in growing nickelate superconductor crystals, resolves the crystal structure in the superconducting state and demonstrates an effective pathway towards achieving higher Tc.

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