Disorder-driven phase transitions of the large q-state Potts model in three dimensions

Phase transitions induced by varying the strength of disorder in the large-q state Potts model in 3d are studied by analytical and numerical methods. By switching on the disorder, the transition stays of first order, but different thermodynamical quantities display essential singularities. Only for strong enough disorder will the transition be soften into a second-order one, in which case the ordered phase becomes non-homogeneous at large scales, while the non-correlated sites percolate the sample. In the critical regime the critical exponents are found universal: beta/v = 0.60(2) and. = 0.73(1).