@article{oai:niigata-u.repo.nii.ac.jp:00002454,
 author = {Takano, Ken-Ichi and Kito, Yoshiya and Ono, Yoshiaki and Sano, Kazuhiro},
 issue = {19},
 journal = {Physical Review Letters, Physical Review Letters},
 month = {Nov},
 note = {A novel nonlinear a model method is proposed for the two-dimensional J1-J2 model, which is extended to include plaquette-type distortion. The nonlinear σ model is properly derived without spoiling the original spin degrees of freedom. A disordered phase is found to continue, without quantum phase transitions, from a frustrated uniform regime to an un frustrated distorted regime. By the continuity and Oshikawa's commensurability condition, the disordered ground states for the uniform J1-J2 model are plaquette states with four-fold degeneracy.},
 pages = {197202-1--197202-4},
 title = {Nonlinear σ model method for the J1-J2 Heisenberg model : Disordered Ground State with Plaquette Symmetry},
 volume = {91},
 year = {2003}
}