s-wave superconductivity from antiferromagnetic spin-fluctuation model for bilayer materials

TL;DR

This paper demonstrates that in bilayer materials, antiferromagnetic spin fluctuations can lead to s-wave superconductivity with opposite signs in different layers, challenging the usual association with d-wave pairing.

Contribution

It introduces a novel s-wave pairing mechanism in bilayer materials driven by antiferromagnetic spin correlations, contrasting with traditional d-wave expectations.

Findings

Bilayer structure favors s-wave pairing with opposite signs in layers.

Electron-phonon interactions modulate the superconducting instability.

Antiferromagnetic correlations are key to the s-wave pairing mechanism.

Abstract

It is usually believed that the spin-fluctuation mechanism for high-temperature superconductivity results in d-wave pairing, and that it is destructive for the conventional phonon-mediated pairing. We show that in bilayer materials, due to nearly perfect antiferromagnetic spin correlations between the planes, the stronger instability is with respect to a superconducting state whose order parameters in the even and odd plane-bands have opposite signs, while having both two-dimensional $s$-symmetry. The interaction of electrons with Raman- (infrared-) active phonons enhances (suppresses) the instability.