Raman response in superconducting multiorbital systems with application to nickelates

TL;DR

This paper investigates the Raman response in superconducting nickelates using multiorbital models to identify pairing symmetries and gap characteristics, aiding understanding of their superconducting mechanism.

Contribution

It provides a detailed analysis of Raman fingerprints for various multiorbital models and pairing symmetries in nickelates, including full multiorbital calculations.

Findings

Raman response varies with pairing symmetry and orbital configuration.

Comparison between full multiorbital and additive models highlights interorbital effects.

Results offer insights into minimal models for nickelate superconductivity.

Abstract

The recent discovery of high-$T_c$ superconductivity in pressurized and thin film nickelates is nowadays one of the most relevant and active topics in solid-state physics. The origin of superconductivity together with the relevance of multiorbital physics are highly discussed issues in this field. Knowledge of the size of the gap and its symmetry is of fundamental interest to uncover the superconducting mechanism at play in the nickelates. Electronic Raman scattering is a powerful tool to investigate the main characteristics of the gap. Here, we investigate the Raman response in the superconducting phase for three different models: Two-orbital models, including $d_{x^2-y^2}$ and $d_{z^2}$ orbitals, with one and two layers; as well as a bilayer model with the $d_{x^2-y^2}$ orbital as the only active one. For each of these models, we consider different pairing symmetries and determine their characteristic fingerprints in the Raman response. For the two-orbital models, we perform full multiorbital calculations including interorbital and intraorbital scattering, and compare the results with those obtained using the additive Raman response where each band is considered separately. Our results should be useful for discussing the minimal model for superconductivity and its pairing symmetry in nickelates. The obtained results and discussions, as well as the presented formalism, are also of general interest for other multiorbital systems.