Two-Dimensional Quantum Magnets — Mean Field and Beyond (original) (raw)

Physics and Chemistry of Materials with Low-Dimensional Structures, 1992

Abstract

ABSTRACT Following the recent interest in path integral approaches to studying the properties of low-dimensional quantum magnets we present an examination of the mean field properties of a two-dimensional quantum magnet, together with a detailed analysis of the validity of mean field theory in determining the phase diagram. We find that there are serious restrictions to the validity of the mean field approximation in these systems, the most important of which is an uncontrolled shifting of the zero of the free energy with respect to local spin rotation. We present a formalism which includes fluctuations beyond the mean field limit so that the problems may, in principle, be dealt with, and the effects of fluctuations on the mean field solutions may also be analysed.

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