Fermi-surface reconstruction involving two Van Hove singularities across the antiferromagnetic transition in BaFe2As2

TL;DR

This study uses angle-resolved photoemission to observe how two Van Hove singularities in BaFe2As2 change across the antiferromagnetic transition, causing a Fermi surface reconstruction that may influence superconductivity.

Contribution

First observation of saddle-point singularities at Z and Gamma points in BaFe2As2 and their role in Fermi surface topology change across the magnetic transition.

Findings

Van Hove singularities shift below Fermi energy with antiferromagnetic order

Fermi surface changes from cylindrical to tear-shaped around kz axis

Singularities may induce instabilities relevant to superconductivity

Abstract

We report an angle-resolved photoemission study of BaFe2As2, a parent compound of iron-based superconductors. Low-energy tunable excitation photons have allowed the first observation of a saddle-point singularity at the Z point, as well as the Gamma point. With antiferromagnetic ordering, both of these two van Hove singularities come down below the Fermi energy, leading to a topological change in the innermost Fermi surface around the kz axis from cylindrical to tear-shaped, as expected from first-principles calculation. These singularities may provide an additional instability for the Fermi surface of the superconductors derived from BaFe2As2.