Doping evolution of spin excitations in La₃₋ₓSrₓNi₂O₇/SrLaAlO₄ superconducting thin films

Summary

Using Ni (L₃)-edge resonant inelastic X-ray scattering (RIXS), this work systematically investigates the evolution of electronic and spin excitations with carrier doping in coherently compressively strained La(3-x)Sr(x)Ni(2)O(7)/SrLaAlO(4) thin films, covering the superconducting ((x = 0, 0.09, 0.21)) and overdoped non-superconducting ((x = 0.38)) regimes. In the superconducting films, dispersive spin excitations persist along the ([H,H]) and ([H,0]) directions, with the dispersion remaining almost doping-independent and exhibiting minimal damping, while the spectral weight only moderately decreases, indicating robust bistripe spin correlations. However, in the non-superconducting film at (x = 0.38), the magnetic response becomes strongly broadened and weakened, accompanied by significantly enhanced damping and a spectral weight reduction of approximately 50%, signaling the collapse of coherent bistripe spin excitations. The simultaneous disappearance of magnetic coherence with superconductivity directly establishes the link between doping-controlled magnetism and superconductivity in layered nickelate thin films.

Materials

• La_3-xSr_xNi₂O₇

Methods

• MBE
• RIXS
• XAS
• transport measurements

Keywords

• spin excitations
• double stripe order
• doping evolution
• magnetic coherence

Highlights

• First systematic RIXS study of spin excitations across the doping phase diagram of bilayer nickelate films.
• Provides direct evidence that coherent double-stripe spin excitations are robust throughout the superconducting dome and collapse when superconductivity is destroyed.
• Demonstrates a clear correlation between magnetic coherence and superconductivity in bilayer nickelates.

Conclusions

• In superconducting films (x≤0.21), dispersive spin excitations persist with nearly doping-independent dispersion and modest spectral weight reduction.
• At x=0.38 (overdoped non-superconducting), magnetic response becomes strongly broadened with enhanced damping and ≈50% lower spectral weight, indicating collapse of coherent double-stripe spin excitations.
• The concomitant suppression of magnetic coherence and superconductivity establishes a direct doping-controlled link between magnetism and superconductivity.
• The 0.4 eV and 1.6 eV electronic excitations weaken at x=0.38, indicating degraded bilayer coherence.

Main claims

• In superconducting films (x ≤ 0.21), dispersive spin excitations persist with nearly doping-independent dispersion and only modest spectral weight reduction, consistent with robust double-stripe correlations.
  • Evidence: abstract: 'dispersive spin excitations persist along both [H,H] and [H,0] with nearly doping-independent undamped dispersions',full_text: DHO fits yield essentially coincident dispersions for all superconducting compositions
• At x = 0.38, the magnetic response becomes strongly broadened and weakened with ≈50% lower spectral weight, indicating collapse of coherent double-stripe spin excitations.
  • Evidence: abstract: 'magnetic response becomes strongly broadened and weakened',full_text: 'integrated magnetic spectral weight is ≈50% lower at x=0.38 than at x=0'
• The concomitant suppression of magnetic coherence and superconductivity establishes a direct doping-controlled link between magnetism and superconductivity.
  • Evidence: abstract: 'concomitant suppression of magnetic coherence and superconductivity establishes a direct doping-controlled link',summary_en states the same correlation

Workflow

• sample_preparation — Compressively strained films are phase pure and coherent.
  • Materials: La_3-xSr_xNi₂O₇/SrLaAlO₄ thin films; x = 0, 0.09, 0.21, 0.38
  • Methods: reactive molecular-beam epitaxy (MBE); shuttered layer-by-layer growth
  • Observations: high crystalline quality confirmed by RSM and XRD
• characterization — RIXS reveals electronic and spin excitations across the superconducting dome.
  • Materials: La_3-xSr_xNi₂O₇/SLAO films
  • Methods: X-ray absorption spectroscopy (XAS); Ni L₃-edge resonant inelastic x-ray scattering (RIXS); temperature-dependent resistivity
  • Observations: Superconductivity for x ≤ 0.21; weakly insulating normal state at x = 0.38; dd-excitation manifold evolves weakly up to x = 0.21
• analysis — Coherent double-stripe spin excitations collapse in the non-superconducting overdoped regime.
  • Materials: RIXS spectra from all four doping levels
  • Methods: damped harmonic oscillator (DHO) response function fitting; linear spin-wave calculations (SpinW)
  • Observations: For x ≤ 0.21: dispersive spin excitations with nearly doping-independent dispersion and modest spectral weight reduction; For x = 0.38: strongly broadened, weakened response, ≈50% lower spectral weight