title: Orbital nature of ferromagnetic magnons in manganites.
abstract: Magnon excitation in a ferromagnetic state of Sm(0.55)Sr(0.45)MnO(3) located on the verge of the metal-insulator transition has been studied in terms of the neutron scattering experiment. The anomalous magnon dispersion with the zone-boundary softening is well described by the Heisenberg model with extended exchange coupling constants J(s). In particular the fourth neighbor coupling J(4) is as large as 0.6 times the nearest neighbor one J(1). Theoretical analysis based on the local density approximation + Hubbard U band calculation reveals that this one-dimensional exchange path is due to the (3z(2)-r(2))-type orbital correlation, in sharp contrast to previous proposals.
authors.affiliation: Institute for Materials Research, Tohoku University, Katahira, Sendai 980-8577, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Endoh
authors.forename: H
authors.initials: H
authors.lastname: Hiraka
authors.forename: Y
authors.initials: Y
authors.lastname: Tomioka
authors.forename: Y
authors.initials: Y
authors.lastname: Tokura
authors.forename: N
authors.initials: N
authors.lastname: Nagaosa
authors.forename: T
authors.initials: T
authors.lastname: Fujiwara