title: Nonlinear sigma model method for the J1-J2 Heisenberg model: disordered ground state with plaquette symmetry.
abstract: A novel nonlinear sigma model method is proposed for the two-dimensional J1-J2 model, which is extended to include plaquette-type distortion. The nonlinear sigma model is properly derived without spoiling the original spin degrees of freedom. The method shows that a single disordered phase continuously extends from a frustrated uniform regime to an unfrustrated distorted regime. By the continuity and Oshikawa's commensurability condition, the disordered ground states for the uniform J1-J2 model are plaquette states with fourfold degeneracy.
authors: Toyota Technological Institute, Tenpaku-ku, Nagoya 468-8511, Japan.
authors: Ken'ichi
authors: K
authors: Takano
authors: Yoshiya
authors: Y
authors: Kito
authors: Yoshiaki
authors: Y
authors: Ono
authors: Kazuhiro
authors: K
authors: Sano