Detecting pairing symmetry of bilayer nickelates using electronic Raman scattering

TL;DR

This study shows that electronic Raman scattering can effectively identify the pairing symmetry and gap structure in bilayer nickelate superconductors, aiding the understanding of their unconventional superconductivity.

Contribution

It demonstrates the capability of Raman response analysis to distinguish pairing symmetries and gap anisotropies in bilayer nickelates, emphasizing multiorbital effects.

Findings

Raman response can differentiate between various pairing symmetries.

Nodal d-wave pairing shows robust low-energy power-law behavior.

Detailed gap anisotropy on the $eta$ pocket can be inferred for $s_{ ext{±}}$-wave pairing.

Abstract

The recent discovery of high-temperature superconductivity in both bulk and thin-film bilayer nickelates La$_3$Ni$_2$O$_7$ has garnered significant attention. However, the corresponding pairing symmetry remains debated in both experiments and theoretical studies due to conflicting experimental evidence from bulk and thin-film materials. In this work, we examine the electronic Raman response across different channels for various pairing symmetries within a two-orbital bilayer model. By comparing Raman susceptibilities obtained from multiorbital and band-additive approaches, we demonstrate that Raman response can distinguish between different pairing symmetries and identify pocket-dependent gap amplitudes for both fully gapped and nodal superconducting states. Specifically, the nodal $d_{x^2-y^2}/d_{xy}$-wave pairing exhibits robust low-energy power-law behavior, distinct from a fully gapped pairing. Additionally, for the $s_{\pm}$-wave pairing, the detailed gap anisotropy on the $\beta$ pocket can be determined. Possible experimental implications are also discussed. Our results highlight the crucial role of multiorbital effects in shaping the Raman spectra and establish electronic Raman scattering as a powerful and symmetry-resolved probe for determining the superconducting gap in unconventional superconductors.