Pressure-Invariant Isotope Effect as Evidence for Electronically Driven Intertwined Order in Pr₄Ni₃O₁₀

摘要

本研究利用μ子自旋旋转技术测量了三层Ruddlesden-Popper型镍氧化物Pr₄Ni₃O₁₀中氧同位素（16O/18O）替代对自旋密度波（SDW）转变的影响。在常压下，16O和18O样品的SDW转变温度分别为158.04 K和159.81 K，呈现有限同位素位移。在液压压力下，两种同位素的转变温度均以几乎相同的速率（约-4.9 K/GPa）线性下降，使得同位素位移随压力基本不变。这一压力无关的同位素效应表明SDW转变主要源于电子关联，而非晶格动力学。结合近期非弹性X射线散射结果未发现声子软化现象，该研究支持三层Ruddlesden-Popper镍氧化物中存在由强自旋相互作用稳定的交织电荷密度波与自旋密度波序的新机制。该发现与铜氧化物中掺杂增强同位素效应的行为形成对比，为理解镍氧化物中密度波序的电子起源及其与超导电性的关系提供了重要约束。

材料

• Pr₄Ni₃O₁₀

方法

• Muon-spin rotation (μSR)
• Raman spectroscopy
• Oxygen isotope substitution
• High-pressure measurements

关键词

• oxygen isotope effect
• spin density wave
• intertwined order
• electronically driven
• charge density wave
• pressure invariant

亮点

• First pressure-dependent isotope effect study in trilayer RP nickelates.
• Provides evidence that the intertwined CDW/SDW transition is electronically driven.
• Contrasts with cuprate isotope effect behavior.

结论

• The SDW transition shows a finite oxygen-isotope shift at ambient pressure (ΔT_SDW = 1.77 K).
• Under hydrostatic pressure, T_SDW decreases linearly at nearly identical rates for both isotope compositions, making the isotope shift pressure-independent.
• The absence of pressure enhancement indicates a predominantly electronic origin of the SDW transition.
• This is consistent with recent inelastic X-ray scattering results showing no phonon softening, suggesting a new regime of intertwined order stabilized by strong spin interactions.

主要论断

• The SDW transition shows a finite oxygen-isotope shift at ambient pressure (ΔT_SDW ≈ 1.77 K).
  • 证据: Abstract,Full text: At ambient pressure, 16T_SDW=158.04(5) K and 18T_SDW=159.81(6) K.
• Under pressure, T_SDW decreases linearly at nearly identical rates for both isotopes, so the isotope shift remains constant.
  • 证据: Abstract,Full text: d16T_SDW/dp=-4.93(5) K/GPa and d18T_SDW/dp=-4.90(7) K/GPa.
• The absence of pressure enhancement of the isotope effect points to a predominantly electronic origin of the SDW transition.
  • 证据: Abstract,Full text: The absence of pressure enhancement… points to a predominantly electronic origin of the SDW transition.

研究流程

• sample_preparation
  • 材料: Pr₄Ni₃O₁₀; 16O/18O isotope substitution
  • 方法: oxygen-isotope exchange
  • 观察: 18O enrichment ≈70%
• muon_SR_measurement
  • 方法: weak-transverse-field μSR; hydrostatic pressure cell
  • 观察: SDW transition temperatures for both isotopes
• Raman_measurement
  • 方法: Raman spectroscopy
  • 观察: oxygen participation in phonon modes
• data_analysis
  • 方法: Fermi function fit to paramagnetic fraction; linear fit of T_SDW vs pressure
  • 观察: dT_SDW/dp nearly identical for both isotopes; isotope shift constant under pressure
• interpretation — The pressure-independent isotope effect indicates an electronic origin of the SDW transition.