LOCALIZED-VERSUS-EXTENDED SPIN FLUCTUATIONS IN QUANTUM ANTIFERROMAGNETS

A recently devised trial wave function for the Heisenberg-Ising model is tested against linear spin waves in the whole anisotropic region. The above wave function is asymptotically exact in the limit of high anisotropy, and is constructed using localized spin fluctuations over Neel states. The structure of this trial state is compared with the one presented by the zero-point state of the linear-spin-wave theory. Striking similarities are found between both, despite that spin waves represent fluctuations that encompass the whole system. A crossover between both approaches near the isotropic point is attributed to a delocalization of spin fluctuations. We present results for one and two dimensions, and compare with exact results or numerical simulations.