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arXiv · 0806.4750

Ab initio Derivation of Low-energy Model for Iron-Based Superconductors LaFeAsO and LaFePO

Kazuma Nakamura·Ryotaro Arita·Masatoshi Imada
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Abstract

Effective Hamiltonians for LaFeAsO and LaFePO are derived from the downfolding scheme based on first-principles calculations and provide insights for newly discovered superconductivity in the family of LnFeAsO$_{1-x}$F$_x$, Ln = La, Ce, Pr, Nd, Sm, and Gd. Extended Hubbard Hamiltonians for five maximally localized Wannier orbitals per Fe are constructed dominantly from five-fold degenerate iron-3$d$ bands. They contain parameters for effective Coulomb and exchange interactions screened by the polarization of other electrons away from the Fermi level. The onsite Coulomb interaction estimated as 2.2-3.3 eV is compared with the transfer integrals between the nearest-neighbor Fe-3$d$ Wannier orbitals, 0.2-0.3 eV, indicating moderately strong electron correlation. The Hund's rule coupling is found to be 0.3-0.6 eV. The derived model offers a firm basis for further studies on physics of this family of materials. The effective models for As and P compounds turn out to have very similar screened interactions with slightly narrower bandwidth for the As compound.

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Kazuma Nakamura, Ryotaro Arita, Masatoshi Imada. 2008-08-20. Ab initio Derivation of Low-energy Model for Iron-Based Superconductors LaFeAsO and LaFePO. https://doi.org/10.1143/jpsj.77.093711

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