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Effective tight-binding model for the iron vacancy ordered AFeSe
We investigate the electronic structure of the ternary iron selenide K%
FeSe by considering the spatial symmetry of the vacancy ordered structure. Based on three orbitals of ,
which are believed to play major physics in iron-based superconductors, an
effective two-dimensional tight binding Hamiltonian is constructed with the
vacancy ordered structure being explicitly included. It is shown that the
constructed band model, when combined with generalized Hubbard interactions,
yields a spin susceptibility which exhibits both the block-checkerboard
antiferromagnetism instability and the stripe antiferromagnetism instability.
In particular, for large Hund's rule couplings, the block-checkerboard
antiferromagnetism wins over the stripe antiferromagnetism, in agreement with
the observation in experiments. We argue that such a model with correct
symmetry and Fermi surface structures should be the starting point to model
KFeSe. The spin fluctuations at =()
suggest that interblock fluctuations of spins might play an important role in
the mechanism of superconductivity occurring in this system.Comment: 9 pages, 4 figure
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