Droplet-like Fermi surfaces in the anti-ferromagnetic phase of EuFe2As2, an Fe-pnictide superconductor parent compound

Using angle-resolved photoemission it is shown that the low-lying electronic states of the iron pnictide parent compound EuFe2As2 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.