Effective Hamiltonian for FeAs based superconductors

Abstract

The recently discovered FeAs-based superconductors show intriguing behavior and unusual dynamics of electrons and holes which occupy the Fe $d$-orbitals and As $4s$ and $4p$ orbitals. Starting from the atomic limit, we carry out a strong coupling expansion to derive an effective hamiltonian that describes the electron and hole behavior. The hopping and the hybridization parameters between the Fe $d$ and As $s$ and $p$-orbitals are obtained by fitting the results of our density-functional-theory calculations to a tight-binding model with nearest-neighbor interactions and a minimal orbital basis. We find that the effective hamiltonian, in the strong on-site Coulomb repulsion limit, operates on three distinct sub-spaces coupled through Hund's rule. The three sub-spaces describe different components (or subsystems): (a) one spanned by the $d_{x^2-y^2}$ Fe orbital; (b) one spanned by the degenerate atomic Fe orbitals $d_{xz}$ and $d_{yz}$; and (c) one spanned by the atomic Fe orbitals $d_{xy}$ and $d_{z^2}$. Each of these Hamiltonians is an extended t-t'-J-J' model and is characterized by different coupling constants and filling factors. For the case of the undoped material the second subspace alone prefers a ground state characterized by a spin-density-wave order similar to that observed in recent experimental studies, while the other two subspaces prefer an antiferromagnetic order. We argue that the observed spin-density-wave order minimizes the ground state energy of the total hamiltonian.

11 pages, 6 figures

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• Properties of a two orbital model for oxypnictide superconductors: Magnetic order, B_2g spin-singlet pairing channel, and its nodal structure
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• Magnetic order in orbital models of the iron pnictides
• Influence of $s_{\pm }$ symmetry on unconventional superconductivity in pnictides above the Pauli limit -- two-band model study
• Magnetic Phase Diagram of a Five-Orbital Hubbard Model in the Real-Space Hartree Fock Approximation Varying the Electronic Density
• The Phase Transition of Square Lattice Antiferromagnets at Finite Temperature
• Tight-binding Hamiltonian for LaOFeAs
• Quantum critical behavior driven by Hund's rule coupling in quantum antiferromagnets
• Is the nature of magnetic order in copper-oxides and in iron-pnictides different?
• Pairing mechanism in Fe pnictide superconductors
• Non-Convergent Perturbation Theory and Misleading Inferences about Parameter Relationships: the Case of Superexchange
• Two-orbital quantum spin model of magnetism in the iron pnictides
• Particular type of gap in the spectrum of multiband superconductors