Pairing symmetry and properties of iron-based high temperature superconductors

TL;DR

This paper classifies pairing symmetries in iron-based high-temperature superconductors, analyzing their quasiparticle gap structures and proposing implications for the pairing mechanism based on group theory and experimental considerations.

Contribution

It provides a comprehensive classification of pairing matrices in orbital space and discusses their physical properties and experimental implications.

Findings

Identified three categories of quasiparticle gaps: full, nodal, and gapless.

Nodal-gap states exhibit the Volovik effect even with on-site pairing.

Gapless states are unstable due to negative superfluid density.

Abstract

Pairing symmetry is important to indentify the pairing mechanism. The analysis becomes particularly timely and important for the newly discovered iron-based multi-orbital superconductors. From group theory point of view we classified all pairing matrices (in the orbital space) that carry irreducible representations of the system. The quasiparticle gap falls into three categories: full, nodal and gapless. The nodal-gap states show conventional Volovik effect even for on-site pairing. The gapless states are odd in orbital space, have a negative superfluid density and are therefore unstable. In connection to experiments we proposed possible pairing states and implications for the pairing mechanism.