Detecting pairing symmetry of bilayer nickelates using electronic Raman scattering

Summary

Using a two-orbital bilayer model, this study systematically calculates the electronic Raman response in different Raman channels via both multiorbital and band-sum methods to distinguish the controversial pairing symmetry in the bilayer nickelate superconductor La₃Ni₂O₇. B_y comparing the Raman susceptibilities obtained from the multiorbital approach and the band-sum approximation, it is found that the Raman response can effectively differentiate various pairing symmetries and identify the Fermi-pocket-dependent gap sizes in fully gapped and nodal superconducting states. Specifically, nodal d_x^2-_y²/d_xy-wave pairing exhibits robust power-law behavior at low energies, distinctly different from fully gapped pairing; for s±-wave pairing, detailed gap anisotropy on the β pocket can be determined. The study also emphasizes the crucial role of multiorbital effects in shaping the Raman spectra, and points out that electronic Raman scattering, as a symmetry-resolving probe, provides a powerful means to determine the superconducting gap structure of unconventional superconductors, offering significant experimental implications for understanding the superconducting mechanism of bilayer nickelates.

Materials

• La₃Ni₂O₇ (bilayer nickelate)

Methods

• Electronic Raman scattering formalism
• Multiorbital approach
• Band-additive approach

Keywords

• pairing symmetry
• raman response
• superconducting gap
• multiorbital effects
• power law behavior

Highlights

• Our results highlight the crucial role of multiorbital effects in shaping the Raman spectra.
• Electronic Raman scattering is established as a powerful and symmetry-resolved probe for determining the superconducting gap in unconventional superconductors.

Conclusions

• Nodal d-wave pairing exhibits robust power-law behavior at low energies, distinctly different from fully gapped pairing.
• For s±-wave pairing, detailed gap anisotropy on the β pocket can be resolved.
• Raman response can effectively differentiate various pairing symmetries and identify Fermi-pocket-dependent gap sizes.

Main claims

• Electronic Raman scattering can effectively distinguish different pairing symmetries in bilayer nickelates, with nodal d-wave pairing showing robust power-law behavior distinct from fully gapped s±-wave pairing.
  • Evidence: Abstract: 'nodal d-wave pairing exhibits robust power-law behavior at low energies, distinctly different from fully gapped pairing; for s±-wave pairing, detailed gap anisotropy on the β pocket can be determined'
• Multiorbital effects play a crucial role in shaping the Raman spectra, and the approach provides a powerful symmetry-resolved probe for the superconducting gap.
  • Evidence: Abstract: 'the study emphasizes the crucial role of multiorbital effects in shaping the Raman spectra, and points out that electronic Raman scattering… provides a powerful means to determine the superconducting gap structure'

Workflow

• Model construction
  • Materials: Bilayer nickelate La₃Ni₂O₇
  • Methods: Two-orbital bilayer tight-binding model; Various pairing symmetries (s±, d-wave)
  • Observations: Three Fermi pockets: α, β, γ
• Raman response calculations — Electronic Raman scattering can distinguish pairing symmetries in bilayer nickelates
  • Materials: Model with superconducting order parameters
  • Methods: Multiorbital and band-additive Raman susceptibility; Effective mass approximation for Raman vertices
  • Observations: Distinct low-energy power-law behaviors for nodal vs fully gapped pairings; Gap anisotropy on β pocket detectable