title: Orbital ordering, new phases, and stripe formation in doped layered nickelates.
abstract: Ground-state properties of layered nickelates are investigated based on the orbital-degenerate Hubbard model coupled with lattice distortions, by using numerical techniques. The Néel state composed of spin S=1 ions is confirmed in the undoped limit x = 0. At x = 1/2, novel antiferromagnetic states, called CE- and E-type phases, are found by increasing the Hund's coupling. (3x2-r2/3y2-r2)-type orbital ordering is predicted to occur in a checkerboard-type charge-ordered state. At x = 1/3, both Coulombic and phononic interactions are found to be important, since the former stabilizes the spin stripe, while the latter leads to the striped charge order.
authors.affiliation: Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Hotta
authors.forename: Elbio
authors.initials: E
authors.lastname: Dagotto