Spin Fluctuations in the Rare-Earth Doped Bilayer Nickelates

摘要

通过非弹性中子散射研究了稀土Pr和Nd掺杂的双层镍酸盐La₂LnNi₂O_7-δ（Ln=La, Pr, Nd）粉末在常压下的自旋涨落。在未掺杂的La₃Ni₂O_7-δ中观测到的45 meV平坦自旋涨落模式，在掺杂后分裂为43和48 meV两个模式，并在约60 meV处出现另一弱模式。其中La₂NdNi₂O_7-δ的自旋涨落强度显著高于La₃Ni₂O_7-δ和La₂PrNi₂O_7-δ。这些结果与基于条纹型反铁磁海森堡模型的描述一致，表明稀土掺杂增强了层间磁耦合，层间交换耦合SJ⊥从约60 meV提升至69–73 meV，层内耦合保持较弱（≤3.5 meV）。这种增强可能解释了稀土掺杂后超导转变温度从80 K升至接近100 K的现象。该工作揭示了稀土掺杂对双层镍酸盐自旋动力学和超导配对的调控作用。

材料

• La₂LnNi₂O₇-δ (Ln=La、Pr、Nd) powder

方法

• Inelastic neutron scattering (INS)
• Linear spin-wave theory
• Heisenberg model

关键词

• spin fluctuations
• interlayer magnetic coupling
• flat spin mode
• rare earth doping
• enhanced tc

亮点

• Our results are consistent with an enhanced interlayer coupling within the stripe-type Heisenberg model framework.
• The stronger spin excitations in La₂NdNi₂O₇-δ probably support higher T_c under pressure than the parent compound.

结论

• Rare-earth doping enhances the interlayer magnetic coupling, with interlayer exchange coupling J⊥ increasing from about 60 meV to 69–73 meV.
• The intralayer coupling remains weak (≤3.5 meV).
• This enhancement may account for the increase in superconducting transition temperature from 80 K to near 100 K following rare-earth doping.

主要论断

• In La₂NdNi₂O₇-δ, the flat spin fluctuation mode at 45 meV splits into two modes at 43 and 48 meV with an additional weak mode at ≈60 meV, and spin fluctuation intensity is significantly higher than in undoped and Pr-doped samples.
  • 证据: Abstract: 'this mode splits into two modes at 43 and 48 meV, with an additional weak mode appearing at approximately 60 meV. Notably, the spin fluctuation intensity in La₂NdNi₂O₇-δ is significantly higher'
• Rare-earth doping enhances interlayer magnetic coupling S⊥J⊥ from ≈60 meV to 69-73 meV, which may account for the increase in T_c from 80 K to near 100 K.
  • 证据: Abstract: 'the interlayer exchange coupling S⊥J⊥ increasing from about 60 meV to 69–73 meV… This enhancement may account for the increase in superconducting transition temperature'

研究流程

• Sample preparation
  • 材料: La₂LnNi₂O₇-δ (Ln=La, Pr, Nd) powder samples
  • 方法: Sol-gel method
  • 观察: Phase purity confirmed, magnetic susceptibility and heat capacity measurements
• Inelastic neutron scattering — Spin fluctuations in Nd-doped sample are stronger than in pure and Pr-doped
  • 材料: Powder samples
  • 方法: Time-of-flight INS on MERLIN and PANTHER spectrometers
  • 观察: CEF excitations at low energies; Flat spin fluctuation mode around 45 meV splits into two modes in doped samples; Additional mode at ≈60 meV
• Theoretical fitting — Enhanced interlayer coupling may account for increased T_c (up to ≈100 K) in rare-earth doped samples
  • 材料: Experimental dispersion
  • 方法: Stripe-type Heisenberg model; Linear spin wave theory (SpinW)
  • 观察: Interlayer coupling S⊥J⊥ increases from ≈60 meV to 69-73 meV upon doping; Intralayer coupling remains weak (≤3.5 meV)