Phase diagram of a two-dimensional large- Q Potts model in an external field

Abstract

We use a two-dimensional Wang–Landau sampling algorithm to map out the phase diagram of a Q-state Potts model with Q ⩽ 10 in an external field H that couples to one state. Finite-size scaling analyses show that for large Q the first-order phase transition point at H = 0 is in fact a triple point at which three first-order phase transition lines meet. One such line is restricted to H = 0 ; another line has H ⩽ 0 . The third line, which starts at the H = 0 triple point, ends at a critical point ( T c , H c ) which needs to be located in a two-dimensional parameter space. The critical field H c ( Q ) is positive and decreases with decreasing Q, which is in qualitative agreement with previous predictions.