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

Summary

Through muon spin rotation/relaxation and resistivity measurements combined with oxygen isotope substitution, the pressure and isotope effects on density wave transitions in the trilayer Ruddlesden-Popper nickelate La₄Ni₃O₁₀ were systematically investigated. Under ambient pressure, two incommensurate spin density wave (SDW) transitions were observed at 132 K and 80–90 K; the magnetic structure reveals that the outer two Ni layers exhibit an antiferromagnetically coupled SDW order, while the inner layer has a smaller magnetic moment, and a c-axis component of the magnetic moment emerges below T*. The abrupt onset of the internal field at T_SDW indicates that the SDW transition resembles a first-order phase change and is closely intertwined with the charge density wave (CDW) occurring at the same temperature. Under applied pressure, T_SDW, T*, and T_CDW are uniformly suppressed at a rate of approximately -13 K/GPa, differing from the behavior in bilayer La₃Ni₂O₇ where pressure increases the separation between SDW and CDW. Substitution of ¹⁶O with ¹⁸O raises T_CDW; in the region where CDW and SDW are intertwined, T_SDW also exhibits a significant isotope effect similar in magnitude to the shift in T_CDW, whereas no isotope effect is observed for the SDW at T* where it evolves independently. These results reveal the strongly intertwined nature of SDW and CDW in La₄Ni₃O₁₀ and suggest that pressure-induced suppression of the CDW order may be a key mechanism for high-pressure superconductivity in Ruddlesden-Popper nickelates.

Materials

• La₄Ni₃O₁₀-δ polycrystalline

Methods

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

Keywords

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

Highlights

• 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.

Conclusions

• 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*.

Main claims

• At ambient pressure, La₄Ni₃O₁₀ exhibits two incommensurate spin-density wave transitions at T_SDW ≈ 132 K and T* ≈ 80-90 K.
  • Evidence: 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.
  • Evidence: 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.
  • Evidence: 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.
  • Evidence: 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.
  • Evidence: 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'

Workflow

• sample_preparation_and_characterization — Samples are well-characterized with controlled oxygen content.
  • Materials: La₄Ni₃O_10-δ polycrystals; ¹⁶O and ¹⁸O isotope-substituted samples
  • Methods: X-ray diffraction; thermogravimetric analysis; neutron powder diffraction; resistivity; Raman spectroscopy
  • Observations: Monoclinic structure; nearly oxygen-stoichiometric; clear Raman isotope shifts
• muon_spin_rotation_experiments — μSR identifies two incommensurate magnetic transitions.
  • Materials: pristine and isotope-substituted La₄Ni₃O₁₀
  • Methods: zero-field (ZF) μSR; weak transverse field (WTF) μSR
  • Observations: 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.
  • Materials: La₄Ni₃O₁₀ under pressure and with isotope substitution
  • Methods: μSR under pressure; resistivity under pressure; μSR on isotope samples
  • Observations: All transition temperatures suppressed at ~-13 K/GPa; ¹⁸O substitution increases T_CDW and intertwined T_SDW, but not T*