Possible pairing states in the superconducting bilayer nickelate

TL;DR

This paper investigates potential pairing mechanisms in bilayer nickelate superconductors, exploring mixed $d$- and $s$-wave states and the influence of magnetic correlations and Fermi surface variations within the BCS framework.

Contribution

It introduces the possibility of mixed $d$- and $s$-wave superconducting states and analyzes their relation to magnetic correlations and Fermi surface differences.

Findings

Mixed $d$- and $s$-wave pairing states are plausible in bilayer nickelates.

Magnetic correlations influence the symmetry and structure of the superconducting gap.

Fermi surface variations significantly affect the pairing instability and gap functions.

Abstract

We examine various possibilities for the pairing mechanisms in the recently discovered bilayer-nickelate superconductor within the Bardeen-Cooper-Schrieffer framework. Unlike earlier studies, where only a pure $d$-wave or sign-changing $s$-wave superconductivity instability was investigated, our study explores the possibilities of mixed-state superconducting instability such as the one involving both $d$- and sign-changing $s$-waves. While assuming that the superconductivity arises because of the magnetic correlations, we examine the nature of the superconducting gap function associated density of states with various possible magnetic correlation wavevectors arising out as a result of multiple pockets owing to the multiple orbitals and bilayer splitting. We also explore the effect of differences in the nature of Fermi surfaces suggested by various studies.