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Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors

Krüger, F; Kumar, S; Zaanen, J; Van den Brink, J; (2009) Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors. Physical Review B , 79 (5) , Article 054504. 10.1103/PhysRevB.79.054504.

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Abstract

We develop an understanding of the anomalous metal state of the parent compounds of recently discovered iron-based superconductors starting from a strong-coupling viewpoint, including orbital degrees of freedom. On the basis of an intermediate-spin (S=1) state for the Fe2+ ions, we derive a Kugel-Khomskii spin-orbital Hamiltonian for the active t2g orbitals. It turns out to be a highly complex model with frustrated spin and orbital interactions. We compute its classical phase diagrams and provide an understanding for the stability of the various phases by investigating its spin-only and orbital-only limits. The experimentally observed spin-stripe state is found to be stable over a wide regime of physical parameters and can be accompanied by three different types of orbital orders. Of these the orbital-ferro and orbital-stripe orders are particularly interesting since they break the in-plane lattice symmetry—a robust feature of the undoped compounds. We compute the magnetic excitation spectra for the effective spin Hamiltonian, observing a strong reduction in the ordered moment, and point out that the proposed orbital ordering pattern can be measured in resonant x-ray diffraction.

Type: Article
Title: Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors
DOI: 10.1103/PhysRevB.79.054504
Publisher version: http://dx.doi.org/10.1103/PhysRevB.79.054504
Language: English
Additional information: Copyright © 2009 The American Physical Society.
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > London Centre for Nanotechnology
URI: http://discovery.ucl.ac.uk/id/eprint/1450193
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