MONTE-CARLO CALCULATION OF THE TRANSITION-TEMPERATURE OF THE ANISOTROPIC 3-DIMENSIONAL XY MODEL

The transition temperature of the spatially anisotropic three-dimensio nal classical XY model is calculated by means of Monte Carlo (MC) simu lations. In the XY model the spins are not restricted to the XY plane, as in the plane rotator model. The results are compared with a self-c onsistent harmonic approximation calculation (SCHA). In two dimensions the inclusion of effect of vortices pushes down the transition temper ature from T-KT/J=1.08, given by the standard SCHA to T-KT/J=0.70, in good agreement with the MC estimate T-KT/J=0.725.