On the theory of the phase transition in the two-dimensional planar spin model

Abstract

It is shown that the scaling equations of Kosterlitz, which describe the phase transition in the two-dimensional planar spin model, can be derived from the earlier theory of Kosterlitz and Thouless (1973). The two theories are therefore fundamentally identical and the difference in the final results is due to an extra mathematical approximation made by Kosterlitz and Thouless.