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

摘要

利用Ni L₃边共振非弹性X射线散射（RIXS），该工作系统研究了在相干压应变La_3-xSr_xNi₂O₇/SrLaAlO₄薄膜中电子与自旋激发随载流子掺杂的演变，覆盖了超导（x=0,0.09,0.21）与过掺杂非超导（x=0.38）区间。在超导薄膜中，色散自旋激发沿[H,H]和[H,0]方向持续存在，色散几乎不随掺杂变化且阻尼很小，谱权重仅适度降低，表明双条纹自旋关联保持稳健。然而在x=0.38的非超导薄膜中，磁响应强烈展宽和减弱，阻尼显著增强，谱权重下降约50%，标志着相干双条纹自旋激发崩溃。磁相干性随超导电性的同步消失，直接建立了层状镍酸盐薄膜中掺杂控制的磁性与超导电性之间的关联。

材料

• La_3-xSr_xNi₂O₇

方法

• MBE
• RIXS
• XAS
• transport measurements

关键词

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

亮点

• 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.

结论

• 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.

主要论断

• 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.
  • 证据: 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.
  • 证据: 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.
  • 证据: abstract: 'concomitant suppression of magnetic coherence and superconductivity establishes a direct doping-controlled link',summary_en states the same correlation

研究流程

• sample_preparation — Compressively strained films are phase pure and coherent.
  • 材料: La_3-xSr_xNi₂O₇/SrLaAlO₄ thin films; x = 0, 0.09, 0.21, 0.38
  • 方法: reactive molecular-beam epitaxy (MBE); shuttered layer-by-layer growth
  • 观察: high crystalline quality confirmed by RSM and XRD
• characterization — RIXS reveals electronic and spin excitations across the superconducting dome.
  • 材料: La_3-xSr_xNi₂O₇/SLAO films
  • 方法: X-ray absorption spectroscopy (XAS); Ni L₃-edge resonant inelastic x-ray scattering (RIXS); temperature-dependent resistivity
  • 观察: 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.
  • 材料: RIXS spectra from all four doping levels
  • 方法: damped harmonic oscillator (DHO) response function fitting; linear spin-wave calculations (SpinW)
  • 观察: 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