Droplet-like Fermi surfaces in the anti-ferromagnetic phase of EuFe$_2$As$_2$, an Fe-pnictide superconductor parent compound

TL;DR

This study reveals that EuFe$_2$As$_2$ exhibits droplet-shaped Fermi surfaces in its antiferromagnetic phase, showing significant electronic structure modifications from the paramagnetic phase, consistent with other experimental data.

Contribution

It provides detailed ARPES evidence of droplet-like Fermi surfaces and band hybridization in EuFe$_2$As$_2$, advancing understanding of its magnetic and electronic properties.

Findings

Fermi surface fragments into small droplets in the antiferromagnetic phase

Strong hybridization of back-folded and non-folded bands opens energy gaps

Results align with quantum oscillation and optical data on similar compounds

Abstract

Using angle resolved photoemission it is shown that the low lying electronic states of the iron pnictide parent compound EuFe$_2$As$_2$ are strongly modified in the magnetically ordered, low temperature, orthorhombic state compared to the tetragonal, paramagnetic case above the spin density wave transition temperature. Back-folded bands, reflected in the orthorhombic/ anti-ferromagnetic Brillouin zone boundary hybridize strongly with the non-folded states, leading to the opening of energy gaps. As a direct consequence, the large Fermi surfaces of the tetragonal phase fragment, the low temperature Fermi surface being comprised of small droplets, built up of electron and hole-like sections. These high resolution ARPES data are therefore in keeping with quantum oscillation and optical data from other undoped pnictide parent compounds.