Dirac nodal pockets in the antiferromagnetic parent phase of FeAs superconductors

TL;DR

This paper demonstrates that small Fermi surface pockets in antiferromagnetic FeAs superconductors are consistent with Dirac fermions, revealing a nodal spin-density wave and providing a platform to study strongly interacting Dirac particles.

Contribution

It identifies Dirac dispersion in the Fermi surface pockets of FeAs superconductors, supporting the presence of a nodal spin-density wave in these materials.

Findings

Fermi surface pockets are consistent with Dirac dispersion.

Existence of a cusp in magnetic quantum oscillation frequencies.

Dirac fermions are significantly slower than in graphene.

Abstract

We show that previously measured small Fermi surface pockets within the antiferromagnetic phase of SrFe2As2 and BaFe2As2 are consistent with a Dirac dispersion modulated by interlayer hopping, giving rise to a Dirac point in k-space and a cusp in the magnetic field angle-dependent magnetic quantum oscillation frequencies. These findings support the existence of a nodal spin-density wave in these materials, which could play an important role in protecting the metallic state against localization effects. The speed of the Dirac fermions in SrFe2As2 and BaFe2As2 is found to be 14-20 times slower than in graphene, suggesting that the pnictides provide a laboratory for exploring the effects of strongly interacting Dirac fermions.