Transition in the two-dimensional step model: A Kosterlitz-Thouless transition in disguise - art. no. 052407

Evidence for a Kosterlitz-Thouless transition in the two-dimensional (2D) s tep model is obtained from Monte Carlo determinations of the helicity modul us. It is argued that the free energy of a single vortex at the center of t he system depends logarithmically on the system size in spite of the fact t hat the spin interaction is not harmonic for small differences in the spin angles. We conclude that this is the reason for the Kosterlitz-Thouless tra nsition in the 2D step model and that the harmonic spin interaction not is a necessary requirement.