Emerging critical behavior at a first-order phase transition rounded by disorder

We investigate the two-dimensional four-color Ashkin-Teller model by means of large-scale Monte-Carlo simulations. We demonstrate that the first-order phase transition of the clean system is destroyed by random disorder introduced via site dilution. The critical behavior of the emerging continuous transition belongs to the clean two-dimensional Ising universality class, apart from logarithmic corrections. These results confirm perturbative renormalization-group predictions; they also agree with recent findings for the three-color case, indicating that the critical behavior is universal.