Density-wave order enhances the phonon thermal Hall effect in a trilayer nickelate

Summary

In the ambient-pressure normal state of the trilayer Ruddlesden-Popper nickelate La₄Ni₃O₁₀, researchers observed a phonon thermal Hall effect enhanced by density-wave order. The material undergoes a density-wave transition at about 140 K, below which the thermal Hall response sharply increases; the thermal Hall angle rises from 1.5‰ at 160 K to 6‰ near 100 K, peaks at ~7‰ at 70 K, and two distinct plateaus appear in the thermal Hall resistivity. The longitudinal thermal conductivity shows almost no magnetic field dependence and has a negligible electronic contribution, confirming that phonons dominate both longitudinal and transverse thermal transport. The characteristic energy extracted from thermal Hall data is about 4.1 meV, which closely matches the magnon–phonon dispersion crossing energy of 3.2 meV, indicating that magnon–phonon hybridization induced by spin-density-wave order is the core mechanism enhancing the thermal Hall effect. This work reveals the significant modulation of phonon transport by spin–lattice coupling in nickelates and points out that such dynamic coupling may participate in suppressing antiferromagnetic order and promoting superconductivity under high pressure via softening of optical phonons, providing a new perspective for understanding the intertwining of charge, spin, and lattice degrees of freedom in unconventional superconductors.

Materials

• La₄Ni₃O₁₀

Methods

• Thermal Hall effect measurement
• Longitudinal thermal conductivity measurement
• Electrical resistivity measurement
• Magnetoresistance measurement
• Wiedemann-Franz law analysis

Keywords

• thermal hall effect
• density wave order
• magnon phonon hybridization
• phonon transport
• spin lattice coupling

Highlights

• We report the first observation of a finite phonon thermal Hall effect in the trilayer nickelate La₄Ni₃O₁₀ at ambient pressure.
• The thermal Hall angle reaches a maximum of nearly 7‰, approximately twice that in cuprates and three times that in SrTiO₃.
• The thermal Hall response is dramatically enhanced below the density-wave transition at ≈140 K, with two distinct plateaus in the thermal Hall resistivity.
• The characteristic energy scale from the thermal Hall response (≈4.1 meV) closely matches the magnon–phonon crossing span (≈3.2 meV), pointing to magnon–phonon hybridization as the primary enhancement mechanism.

Conclusions

• In La₄Ni₃O₁₀, we observe an enhanced phonon thermal Hall effect tied to the density-wave transition.
• We propose that spin-lattice coupling (magnon-phonon hybridization) from SDW order drives both the thermal Hall enhancement and the suppression of long-range antiferromagnetism.
• Thus, La₄Ni₃O₁₀ exemplifies intertwined charge, spin, and lattice orders, where phonons dressed by electronic order play an active role in the normal state of superconducting nickelates.

Main claims

• A finite phonon thermal Hall effect is observed in La₄Ni₃O₁₀ at ambient pressure, strongly enhanced below the density-wave transition at ≈140 K.
  • Evidence: κxy/κxx increases from 1.5‰ at 160 K to 6‰ at 100 K, peaks at ≈7‰ at 70 K,two distinct plateaus in thermal Hall resistivity below T*
• The thermal Hall signal is overwhelmingly phononic, not electronic.
  • Evidence: κxx shows almost no magnetic field dependence at 0 T vs 10 T,electronic contribution estimated from Wiedemann-Franz law is one to two orders of magnitude smaller than measured κxy
• The characteristic energy scale of the enhanced thermal Hall effect (≈4.1 meV) matches the magnon–phonon crossing energy (≈3.2 meV), indicating magnon–phonon hybridization as the underlying mechanism.
  • Evidence: fit of λxy gives T₀ = 48 K (4.1 meV),calculated phonon-magnon crossing span is 3.2 meV
• Magnon–phonon hybridization may also assist in destabilizing the spin-density-wave order under pressure and facilitate superconductivity.
  • Evidence: speculative argument based on optical phonon softening under pressure,analogy to cuprates

Workflow

• measurement — A phononic thermal Hall effect is observed and strongly enhanced below the density-wave transition.
  • Materials: La₄Ni₃O₁₀ single crystals
  • Methods: resistivity; magnetoresistance up to 55T; longitudinal and transverse thermal conductivity in magnetic field; thermal Hall angle extraction
  • Observations: resistivity upturn and kink at ≈140 K indicating DW transition; thermal Hall angle κxy/κxx rises from 1.5‰ at 160 K to 6‰ at 100 K, peaks ≈7‰ at 70K; two plateaus in thermal Hall resistivity λxy; κxx nearly field-independent, electronic κxy contribution negligible
• analysis — The extracted characteristic energy matches the magnon–phonon crossing energy, pointing to magnon–phonon hybridization as the origin of the enhanced thermal Hall effect.
  • Methods: comparison of measured κxy/T with electronic estimate from Wiedemann-Franz law; extraction of characteristic temperature T₀ from fit of λxy = λ0 * tanh(T₀/T); comparison with calculated phonon and magnon dispersions
  • Observations: characteristic energyT₀ = 48 K → 4.1 meV; magnon-phonon crossing span = 3.2 meV (and 1.4 meV); close correspondence of energy scales
• interpretation — Magnon–phonon hybridization due to spin-density-wave order is the primary mechanism for the enhanced phonon thermal Hall effect, and this coupling may soften optical phonons under pressure to suppress antiferromagnetism and promote superconductivity.
  • Methods: physical argument that SDW order introduces magnon bands hybridizing with phonons, imparting Berry curvature
  • Observations: observed SDW and magnon bands in La₄Ni₃O₁₀ from prior studies