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


Kruger, Frank and Kumar, Sanjeev and Zaanen, Jan and Brink van den, Jeroen (2009) Spin-orbital frustrations and anomalous metallic state in iron-pnictide superconductors. Physical Review B: Condensed matter and materials physics, 79 (5). 054504. ISSN 1098-0121

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.
Item Type:Article
Copyright:© 2009 American Physical Society
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Link to this item:http://purl.utwente.nl/publications/61379
Official URL:http://dx.doi.org/10.1103/PhysRevB.79.054504
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