title: Unified origin for the 3D magnetism and superconductivity in NaxCoO2.
abstract: We analyze the origin of the three-dimensional (3D) magnetism observed in nonhydrated Na-rich Na(x)CoO2 within an itinerant spin picture using a 3D Hubbard model. The origin is identified as the 3D nesting between the inner and outer portions of the Fermi surface, which arise due to the local minimum structure of the a(1g) band at the Gamma-A line. The calculated spin wave dispersion strikingly resembles the neutron scattering result. We argue that this 3D magnetism and the spin fluctuations responsible for superconductivity in the hydrated systems share essentially the same origin.
authors.affiliation: Department of Applied Physics and Chemistry, The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Kuroki
authors.forename: Shuhei
authors.initials: S
authors.lastname: Ohkubo
authors.forename: Takumi
authors.initials: T
authors.lastname: Nojima
authors.forename: Ryotaro
authors.initials: R
authors.lastname: Arita
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Onari
authors.forename: Yukio
authors.initials: Y
authors.lastname: Tanaka