Quantum Effects in Two-Dimensional X-Y Model

Abstract

Quantum effects in the two-dimensional X-Y model are discussed keeping in mind the problem whether the quantum X-Y model in two dimensions shows the Kosterlitz-Thouless transition, which is driven by the appearance of topological disorder in the spin configuration, as the classical X-Y model. Quantum effects are treated as perturbations to the classical model, which corresponds to the limit that the magnitude of spin S→∞, by using the 1/s-expansion, where s = [ S(S+1) ]^1/2.