Collective Spin Modes in Superconducting Double Layers

TL;DR

This paper explores collective spin excitations in a superconducting double layer system, revealing how antiferromagnetic polarization induces a novel spin-triplet pairing and results in a Goldstone mode below the particle-hole threshold.

Contribution

It demonstrates the emergence of an undamped collective mode due to antiferromagnetic polarization inducing spin-triplet pairing in a superconducting double layer.

Findings

Antiferromagnetic spin polarization induces spin-triplet pairing.

A Goldstone mode appears below the particle-hole threshold.

The mode is undamped and interpreted as a Goldstone excitation.

Abstract

We investigate a double layer system with tight-binding hopping, intra-layer and inter-layer interactions, as well as a Josephson like coupling. We find that an antiferromagnetic spin polarization induces additional spin-triplet pairing (with $S_z =0$) to the singlet order parameter. This causes an undamped collective mode in the superconducting state below the particle-hole threshold, which is interpreted as a Goldstone excitation.