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

¹  Van der Waals-Zeeman Institute, University of Amsterdam - NL-1018XE Amsterdam, The Netherlands, EU
²  Helmholtz Zentrum Berlin - Albert-Einstein-Strasse 15, 12489 Berlin, Germany, EU
³  Leibniz Institute of Solid and Materials Research Dresden - P.O. Box 270116, D-01171, Dresden, Germany, EU
⁴  Institut für Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Universität 55099 Mainz, Germany, EU
⁵  I. Physikalisches Institut, Georg-August-Universität - Göttingen 37077, Germany, EU
⁶  Walther-Meissner-Institut - Walther-Meißner Strasse 8, 85748 Garching, Germany, EU
⁷  Paul Scherrer Institut, Swiss Light Source - 5232 Villigen, Switzerland

Corresponding author: s.dejong1@uva.nl

Received: 17 December 2009
Accepted: 11 January 2010

Abstract

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.