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

Research output: Contribution to journalResearch articleContributedpeer-review

Contributors

  • Frank Krüger - , University of Illinois at Urbana-Champaign (Author)
  • Sanjeev Kumar - , Leiden University, University of Twente (Author)
  • Jan Zaanen - , Leiden University (Author)
  • Jeroen Van Den Brink - , Leiden University, Radboud University Nijmegen (Author)

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.

Details

Original languageEnglish
Article number054504
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume79
Issue number5
Publication statusPublished - 2 Feb 2009
Peer-reviewedYes
Externally publishedYes