INCOMMENSURATE CORRELATIONS IN QUANTUM SPIN MODELS

Frustrated quantum antiferromagnets in two dimensions are studied by analyzing, using a 1/N expansion, the phase properties of associated (2 + 1)-dimensional nonlinear continuum models. The spin system on square lattice with isotropic couplings that include up to the third-nearest neighbors is considered. Periodic, commensurate, or incommensurate correlations are found to be stable. The relevance in some phase regions of effective (1 + 1)-dimensional nonlinear models is discussed.