Superconducting phase diagram of multi-layer square-planar nickelates

摘要

本研究系统构建了多层方形平面镍酸盐Ndn+1Ni_nO₂n+2（n=4–8）的超导相图，发现n=4至7的化合物呈现超导转变迹象，起始临界温度最高达12.9 K（n=6），n=8仅显示微弱超导关联。通过降低层数n，超导各向异性因钕位4f电子效应发生反转——电子结构趋近铜酸盐特性，且磁涨落在超导区及过掺杂非超导区持续存在。值得注意的是，该超导区与化学掺杂无限层镍酸盐重叠，揭示了不同结构实现在方形平面镍酸盐中的共性与差异。这一工作确立了通过原子精度层状设计合成新型镍基超导体的通用模板。

材料

• Nd₄Ni₃O₈
• Nd₅Ni₄O₁₀
• Nd₆Ni₅O₁₂
• Nd₇Ni₆O₁₄
• Nd₈Ni₇O₁₆
• Nd₉Ni₈O₁₈

方法

• MBE
• topotactic reduction
• XRD
• STEM
• transport measurements
• RIXS

关键词

• square planar nickelates
• superconducting dome
• magnetic fluctuations
• cuprate like electronic structure

亮点

• Constructs the first comprehensive phase diagram of multi-layer square-planar nickelates.
• Shows that structural tuning via layering provides a unique knob to access the overdoped regime.
• Observes that magnetic excitations are robust and persist even after superconductivity is destroyed.

结论

• Superconductivity is observed in Nd_n+1Ni_nO₂n+2 compounds for n=4-8, with maximal T_c up to 12.9 K for n=6.
• The superconducting regime overlaps with chemically-doped infinite-layer nickelates, showing a universal doping region near 3d9.
• Decreasing n enhances cuprate-like electronic structure (increased O-Ni hybridization, reduced Nd-Ni hybridization).
• Magnetic fluctuations persist from the superconducting regime into the overdoped non-superconducting regime (n=3).
• The 4f moments of Nd affect the superconducting anisotropy, reversing the expected behavior with decreasing n.

主要论断

• Superconductivity observed in Ndn+1Ni_nO₂n+2 for n=4-8 with maximal T_c12.9 K at n=6
  • 证据: From abstract: 'construct a phase diagram of multi-layer square-planar Ndn+1Ni_nO₂n+2 compounds and discover signatures of superconductivity for n = 4 - 8',From abstract: 'The maximal observed T_c,onset occurs at 12.9 K in n=6'
• Superconducting regime overlaps with chemically-doped infinite-layer nickelates
  • 证据: From abstract: 'superconducting regime overlaps with that of chemically-doped infinite-layer nickelates'
• Magnetic excitations persist into overdoped non-superconducting regime
  • 证据: From abstract: 'magnetic fluctuations persist from within the superconducting regime and into the over-doped, non-superconducting regime'

研究流程

• thin_film_growth — Entire series of Ndn+1Ni_nO₂n+2 compounds synthesized
  • 材料: Ndn+1Ni_nO₃n+1 precursors
  • 方法: oxide molecular beam epitaxy; topotactic reduction with CaH₂
  • 观察: epitaxial multi-layer square-planar nickelate films
• structural_characterization — Atomically precise layered structure with local lattice expansion near fluorite layers
  • 材料: Ndn+1Ni_nO₂n+2 films
  • 方法: X-ray diffraction; scanning transmission electron microscopy
  • 观察: crystal structure; lattice constants; local lattice expansion
• transport_measurements — Superconductivity observed for n=4-7 with maximal T_c12.9 K at n=6
  • 材料: Ndn+1Ni_nO₂n+2 films
  • 方法: four-probe resistivity; angle-dependent magnetoresistance
  • 观察: superconducting transitions; anisotropy
• resonant_inelastic_x-ray_scattering — Magnetic excitations persist from superconducting n=5 to overdoped non-superconducting n=3
  • 材料: Ndn+1Ni_nO₂n+2 films
  • 方法: RIXS at Ni L₃ edge
  • 观察: orbital excitations; magnetic excitations