Binder's cumulant for the Kosterlitz-Thouless transition

It is shown that Binder's cumulant U = 1- M 4 / 3 M 2 2 is very useful in the study of the Kosterlitz-Thouless transition of two-dimensional XY systems. It is possible to calculate the critical exponent without knowledge of the critical temperature, and to exclude the possibility of a power law behaviour.