Effect of Pressure and Oxygen-Isotope Substitution on Density-Wave Transitions in La₄Ni₃O₁₀

摘要

通过μ子自旋旋转/弛豫和电阻率测量，结合氧同位素替代，系统研究了三层Ruddlesden-Popper镍酸盐La₄Ni₃O₁₀中密度波转变的压力和同位素效应。常压下观察到两个不相称自旋密度波（SDW）转变，分别发生在132 K和80-90 K；磁结构显示外层两个Ni层呈反铁磁耦合SDW序，内层磁矩较小，且在T*以下磁矩出现c轴分量。TSDW处内场突现表明SDW转变类似于一级相变，并与同一温度发生的电荷密度波（CDW）紧密交织。施加压力后，TSDW、T*和TCDW均以约-13 K/GPa的速率均匀抑制，不同于双层La₃Ni₂O₇中压力增大SDW与CDW间距的行为。¹⁶O→¹⁸O替代使TCDW升高；在CDW与SDW交织区域，TSDW亦呈现显著同位素效应且与TCDW位移相近，而在T*处SDW独立演化时则无同位素效应。这些结果揭示了La₄Ni₃O₁₀中SDW与CDW的强交织本质，并指出压力诱导CDW序的抑制可能是Ruddlesden-Popper镍酸盐中高压超导的关键机制。

材料

• La₄Ni₃O₁₀-δ polycrystalline

方法

• muon-spin rotation/relaxation (μSR)
• resistivity measurements
• X-ray diffraction
• thermogravimetric analysis
• Raman spectroscopy
• high-pressure μSR and resistivity
• oxygen-isotope substitution

关键词

• spin density wave
• charge density wave
• oxygen isotope effect
• pressure suppression
• intertwined orders
• magnetic structure
• first order transition
• muon stopping site
• dipole field calculations

亮点

• The internal fields at the muon stopping sites appear abruptly at TSDW, suggesting a first-order-like SDW transition closely linked to the CDW order at the same temperature.
• Comparison with dipole-field calculations reveals a magnetic structure with antiferromagnetically coupled SDW order on outer Ni layers and smaller moments on the inner layer.
• The pressure-enhanced difference between TSDW and T* suggests that magnetic fluctuations are effectively enhanced under pressure.

结论

• At ambient pressure, two incommensurate SDW transitions are identified at TSDW≈132 K and T*≈80-90 K.
• Under applied pressure, all transition temperatures (TSDW, T*, TCDW) are suppressed at a nearly uniform rate of ~-13 K/GPa.
• Oxygen-isotope substitution shifts TCDW to higher values, and when CDW and SDW are intertwined, a notable isotope effect is observed on TSDW, whereas no isotope effect is detected at T*.

主要论断

• At ambient pressure, La₄Ni₃O₁₀ exhibits two incommensurate spin-density wave transitions at T_SDW ≈ 132 K and T* ≈ 80-90 K.
  • 证据: abstract: 'two incommensurate spin-density-wave (SDW) transitions are identified at T_SDW ≃ 132 K and T* ≃ 80-90 K',full_text Fig. 2f,g show magnetic volume fraction and internal fields with transitions at these temperatures
• The magnetic structure has antiferromagnetically coupled SDW order on outer Ni layers with smaller moments on the inner layer; moments lie in ab-plane above T* but develop c-axis component below.
  • 证据: abstract: 'magnetic structure consistent with antiferromagnetically coupled SDW order on the outer two Ni layers' and 'moments lie mainly in the ab plane, whereas below this temperature they develop a c-axis component',full_text dipole-field calculations and comparison with experimental spectra
• Under pressure, all transition temperatures are suppressed at a nearly uniform rate of ~-13 K/GPa, in contrast to bilayer La₃Ni₂O₇ where pressure separates SDW and CDW.
  • 证据: abstract: 'Under applied pressure, all transition temperatures are suppressed at a nearly uniform rate of ≃-13 K/GPa',full_text Fig. 4e shows linear pressure dependence of T_SDW, T* and T_CDW
• Oxygen isotope substitution (¹⁶O→¹⁸O) increases T_CDW and intertwined T_SDW with nearly identical shift, but T* shows no isotope effect, distinguishing the nature of the two SDW transitions.
  • 证据: abstract: 'a notable isotope effect is observed on T_SDW, yielding nearly identical isotope shifts for T_CDW and T_SDW, whereas no isotope effect is detected at T*',full_text Fig. 8h,i show T* fits yielding negligible isotope shift; Table 4 quantifies shifts
• Pressure-induced suppression of CDW order may be a key mechanism for high-pressure superconductivity in Ruddlesden-Popper nickelates.
  • 证据: abstract: 'the pressure-induced suppression of the CDW order may be a key mechanism for high-pressure superconductivity',full_text: 'if the behavior of the density wave transitions persists at higher pressures, the pressure-induced suppression of CDW order may be a possible mechanism'

研究流程

• sample_preparation_and_characterization — Samples are well-characterized with controlled oxygen content.
  • 材料: La₄Ni₃O_10-δ polycrystals; ¹⁶O and ¹⁸O isotope-substituted samples
  • 方法: X-ray diffraction; thermogravimetric analysis; neutron powder diffraction; resistivity; Raman spectroscopy
  • 观察: Monoclinic structure; nearly oxygen-stoichiometric; clear Raman isotope shifts
• muon_spin_rotation_experiments — μSR identifies two incommensurate magnetic transitions.
  • 材料: pristine and isotope-substituted La₄Ni₃O₁₀
  • 方法: zero-field (ZF) μSR; weak transverse field (WTF) μSR
  • 观察: Two SDW transitions at T_SDW ≈ 132 K and T* ≈ 80-90K; Internal fields appear abruptly at T_SDW; Five-peak to two-peak structure change at T*
• high_pressure_and_isotope_studies — Pressure suppresses all DW transitions uniformly; isotope effect distinguishes intertwined vs independent transitions.
  • 材料: La₄Ni₃O₁₀ under pressure and with isotope substitution
  • 方法: μSR under pressure; resistivity under pressure; μSR on isotope samples
  • 观察: All transition temperatures suppressed at ~-13 K/GPa; ¹⁸O substitution increases T_CDW and intertwined T_SDW, but not T*