Phase transition in the two-dimensional $q$-state Potts model with random ferromagnetic couplings in the large-q limit is conjectured to be described by the isotropic version of the infinite randomness fixed point of the random transverse-field Ising spin chain. This is supported by extensive numerical studies with a combinatorial optimization algorithm giving estimates for the critical exponents in accordance with the conjectured values: $\beta=(3-\sqrt{ 5})/4$, $\beta_s=1/2$ and $\nu=1$. The specific heat has a logarithmic singularity, but at the transition point there are very strong sample-to-sample fluctuations. Discretized randomness results in discontinuities in the internal energy.
Categories: cond-mat.stat-mech cond-mat.dis-nn