Raman response in superconducting multiorbital systems with application to nickelates

Summary

This study systematically analyzes the Raman response of superconducting multi-orbital systems using electronic Raman scattering methods, with nickelates as the application target. For three models—a single-layer and a bilayer two-orbital model involving dx2-y2 and dz2 orbitals, and a bilayer single-orbital model with only dx2-y2 orbitals—multiple pairing symmetries including d-wave, s±-wave, and s-wave are considered, and the response characteristics under various Raman symmetries (A₁g, B₁g, B₂g) are calculated. In the two-orbital models, a full multi-orbital approach is employed, incorporating both intra-orbital and inter-orbital scattering, and compared with the additive approximation that simply sums the Raman responses of individual bands. The results reveal distinct fingerprint features in the Raman spectra for different pairing symmetries and model structures, with the full multi-orbital calculations uncovering inter-orbital mixing effects that the additive approximation may overlook. These findings help clarify the minimal model for nickelate superconductivity, determine the magnitude and symmetry of their superconducting gaps, and provide a general theoretical framework for Raman experimental analysis of other multi-orbital superconductors, such as iron-based superconductors.

Materials

• La₃Ni₂O₇
• La₄Ni₃O₁₀

Methods

• electronic Raman scattering calculations
• multiorbital formalism

Keywords

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

Highlights

• 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.

Conclusions

• 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.

Main claims

• Raman spectra can distinguish between different pairing symmetries and minimal models for nickelate superconductivity
  • Evidence: 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

Workflow

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