Neutron scattering and superconducting order parameter in YBa2Cu3O7

TL;DR

This paper investigates the neutron scattering peak in YBa2Cu3O7 and suggests it is due to spin-flip excitations across an s-wave superconducting gap with opposite signs in bilayer bands.

Contribution

It proposes that the neutron scattering peak is best explained by an s-wave order parameter with sign change between bilayer bands in YBa2Cu3O7.

Findings

Peak explained by spin-flip excitations across the gap

Supports s-wave symmetry with sign change in bilayer bands

Enhancement by antiferromagnetic interactions

Abstract

We discuss the origin of the neutron scattering peak at 41 meV observed in YBa$_2$Cu$_3$O$_7$ below $T_c$. The peak may occur due to spin-flip electron excitations across the superconducting gap which are enhanced by the antiferromagnetic interaction between Cu spins. In this picture, the experiment is most naturally explained if the superconducting order parameter has $s$-wave symmetry and opposite signs in the bonding and antibonding electron bands formed within a Cu$_2$O$_4$ bilayer.