ORDER-PARAMETER DISTRIBUTION FUNCTION AND ORDER OF THE PHASE-TRANSITION OF THE FERROMAGNETIC POTTS-MODEL

The order-parameter distribution functions (OPDF) of the ferromagnetic three-state Potts model in d = 2 and 3 are studied by means of the Monte Carlo simulation. We investigate the difference between the behavior of OPDF for the vector order parameter and that for the scalar order parameter. The OPDF for the scalar order parameter show a double-peak structure not only at the first-order phase transition but also at the second-order one. The origin of the above fictitious double-peak structure, which does not appear in OPDF for the vector order parameter at the second-order transition, is discussed in connection with the structure of the order-parameter space.