J1-J2model: Energy, correlations, and order-parameter fluctuations on finite lattices

Abstract
A modified spin-wave theory is applied to frustrated quantum antiferromagnets on finite square lattices. The results for the energy and for the correlation functions are found to agree very well with exact values obtained by numerical methods. The fluctuations of different order parameters, previously proposed to characterize possible different phases of purely quantum origin, are investigated. Our results suggest that the enhancement of long-range dimer and twist order seen numerically is not significant, and is due to the finite size of the lattices considered.