title: Ferro-orbital order and strong magnetic anisotropy in the parent compounds of iron-pnictide superconductors.
abstract: The puzzling nature of magnetic and lattice phase transitions of iron pnictides is investigated via a first-principles Wannier function analysis of representative parent compound LaOFeAs. A rare ferro-orbital ordering is found to give rise to the recently observed highly anisotropic magnetic coupling, and drive both phase transitions--without resorting to widely employed frustration or nesting picture. The revealed necessity of the additional orbital physics leads to a correlated electronic structure fundamentally distinct from that of the cuprates. In particular, the strong coupling to the magnons advocates active roles of light orbitons in spin dynamics and electron pairing in iron pnictides.
authors.affiliation: Condensed Matter Physics and Materials Science Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
authors.forename: Chi-Cheng
authors.initials: CC
authors.lastname: Lee
authors.forename: Wei-Guo
authors.initials: WG
authors.lastname: Yin
authors.forename: Wei
authors.initials: W
authors.lastname: Ku