Layer Architecture Shapes Electronic, Magnetic, and Lattice Interactions in Ruddlesden-Popper Nickelates

Summary

We performed a systematic comparison of the two polytypes of La₃Ni₂O₇—the alternating monolayer-trilayer LNO-1313 and the bilayer LNO-2222—and the trilayer compound La₄Ni₃O₁₀ using Ni L₃-edge and O K-edge resonant inelastic X-ray scattering (RIXS). We find that the electronic, magnetic, and lattice excitations of LNO-1313 and La₄Ni₃O₁₀ are highly similar, whereas bilayer LNO-2222 exhibits distinctly different features. Compared with LNO-2222, LNO-1313 and La₄Ni₃O₁₀ possess weaker orbital polarization, enhanced 3d8 L (ligand-hole) character, a smaller out-of-plane magnetic exchange scale, and stronger electron-phonon coupling. Within an effective local-moment framework, the spin excitations arising from strong antiferromagnetic interlayer coupling can be naturally described by an entangled-dimer picture, whose advantage is most evident in bilayer LNO-2222, where the interlayer coupling exceeds the intralayer interactions. These results provide key experimental constraints for theoretical models of the low-energy physics relevant to superconductivity in layered nickelates.

Materials

• La₃Ni₂O₇ alternating monolayer-trilayer (LNO-1313)
• La₃Ni₂O₇ bilayer (LNO-2222)
• La₄Ni₃O₁₀

Methods

• resonant inelastic x-ray scattering (RIXS)
• Ni L₃-edge RIXS
• O K-edge RIXS
• x-ray diffraction (XRD)
• high-pressure floating-zone crystal growth
• damped harmonic oscillator (DHO) fitting
• Heisenberg Hamiltonian modeling
• entangled-unit generalized spin-wave calculations

Keywords

• superconductivity
• magnetic excitations
• electron phonon coupling
• orbital polarization
• charge transfer excitations
• spin charge stripe order
• interlayer antiferromagnetic coupling
• entangled dimer scenario
• ligand hole character

Highlights

• First comprehensive RIXS characterization of LNO-1313 spanning electronic, magnetic, and lattice excitations.
• First momentum-resolved RIXS evidence that magnetic correlations in LNO-1313 more closely resemble those of trilayer La₄Ni₃O₁₀ than those of bilayer LNO-2222.
• O K-edge RIXS identifies bond-buckling and bond-stretching phonon modes in nickelates for the first time.
• Unusually pronounced bond-stretching phonon overtones up to eight times the phonon energy in La₄Ni₃O₁₀ indicate very strong electron-phonon coupling.
• The entangled-dimer formalism captures both magnetic-excitation dispersion and spectral-weight momentum dependence, outperforming conventional spin-wave theory especially in LNO-2222.

Conclusions

• RIXS measurements provide a comparative view of electronic, magnetic, and lattice excitations in bilayer LNO-2222, alternating monolayer-trilayer LNO-1313, and trilayer La₄Ni₃O₁₀.
• The bilayer compound exhibits excitation spectra that differ from those of the other two materials, whereas the layer-alternating and trilayer compounds show unexpectedly similar responses across all three excitation channels.
• Compared with LNO-2222, LNO-1313 and La₄Ni₃O₁₀ have weaker orbital polarization, enhanced 3d8L character, a reduced out-of-plane magnetic-exchange scale, and stronger electron-phonon coupling.
• The magnetic excitations in LNO-2222 are better described as triplons than as conventional magnons within an entangled-dimer and spin-charge stripe framework.
• Layer architecture plays a central role in shaping the coupled electronic, magnetic, and lattice degrees of freedom of Ruddlesden-Popper nickelates.

Main claims

Not available in this batch.

Workflow

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