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

• Published in: Journal of the Physical Society of Japan 2008-09, Vol.77 (9), p.93711
• Main Authors: NAKAMURA, Kazuma, ARITA, Ryotaro, IMADA, Masatoshi
• Format: Article
• Language: English
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electronic structure; Exact sciences and technology; Metals, alloys and compounds (a15, 001c15, laves phases, chevrel phases, borocarbides, etc.); Physics; Properties of type I and type II superconductors; Superconducting materials (excluding high-tc compounds); Superconductivity
• ISSN: 0031-9015; 1347-4073
• DOI: 10.1143/jpsj.77.093711

Effective Hamiltonians for LaFeAsO and LaFePO are derived from the downfolding scheme based on first-principles calculations and provide insights for newly discovered superconductors in the family of LnFeAsO1-xFx, 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-3d 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-3d 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.