Raman response in superconducting multiorbital systems with application to nickelates

摘要

本研究利用电子拉曼散射方法，系统分析了超导多轨道系统的拉曼响应，并以镍酸盐为应用对象。针对三种模型——包含dx2-y2和dz2轨道的单层与双层两轨道模型，以及仅含dx2-y2轨道的双层单轨道模型——分别考虑了d波、s±波和s波等多种配对对称性，计算了不同拉曼对称性（A₁g、B₁g、B₂g）下的响应特征。在两轨道模型中，采用了全多轨道方法，同时计入轨道内和轨道间散射，并与将各能带拉曼响应简单相加的加性近似进行了对比。研究发现，不同配对对称性和模型结构在拉曼谱中产生独特的指纹特征，全多轨道计算揭示了加性近似可能忽略的轨道间混合效应。这些结果有助于厘清镍酸盐超导的最小模型，判断其超导能隙的大小与对称性，并为其他多轨道超导体（如铁基超导体）的拉曼实验分析提供了通用的理论框架。

材料

• La₃Ni₂O₇
• La₄Ni₃O₁₀

方法

• electronic Raman scattering calculations
• multiorbital formalism

关键词

• raman response
• pairing symmetry
• inter orbital mixing
• fingerprint features

亮点

• The results help clarify the minimal model for nickelate superconductivity and determine gap magnitude and symmetry.
• The formalism is generally applicable to other multiorbital superconductors like iron-based superconductors.

结论

• Distinct fingerprint features in Raman spectra for different pairing symmetries and model structures are identified.
• Full multiorbital calculations uncover inter-orbital mixing effects that the additive approximation may overlook.

主要论断

• Raman spectra can distinguish between different pairing symmetries and minimal models for nickelate superconductivity
  • 证据: Calculated A₁g and B₁g responses show distinct features for s-wave, s±-wave, and d-wave pairing; full MO calculation reveals inter-orbital mixing effects not captured by additive approximation

研究流程

• Model construction — Different fingerprints for different models and pairing symmetries
  • 材料: Single-layer two-orbital model, bilayer two-orbital model, bilayer one-orbital model
  • 方法: Full multiorbital (MO) Raman response formalism; Additive Raman response (IB) approximation
  • 观察: Raman spectra regarding A₁g, B₁g, B₂g channels