Phase Transitions In Two Planar Lattice Models And Topological Defects:   A Monte Carlo Study
  Monte Carlo simulation has been performed in the planar P(_{2}) and P(_{4}) models to investigate the effects of the suppression of topological defects on the phase transition exhibited by these models. Suppression of the 1/2-defects on the square plaquettes in the P(_{2}) model leads to complete elimination of the phase transition observed in this model. However in the P(_{4}) model, on suppressing the single 1/2-defects on square plaquettes, the otherwise first order phase transition changes to a second order one which occurs at a higher temperature and this is due to presence of large number of 1/2-pair defects which are left within the square plaquettes. When we suppressed these charges too, complete elimination of phase transition was observed. 
Subhrajit Dutta and Soumen Kumar Roy