Nonlinear sigma model method for the J1-J2 Heisenberg model: disordered ground state with plaquette symmetry.
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.
Takano
Ken'ichi
K
Toyota Technological Institute, Tenpaku-ku, Nagoya 468-8511, Japan.
Kito
Yoshiya
Y
Ono
Yoshiaki
Y
Sano
Kazuhiro
K