Effect of random quenched impurities on the critical behavior of a four-state Potts system in two dimensions: An experimental study

Critical behavior of the order-disorder phase transition of the (2×2)-2H structure on Ni(111) was investigated for the pure system and in the presence of 0.3%–3% of a monolayer of preadsorbed atomic oxygen. Depending on oxygen concentration, the values of the critical exponents β, γ, and ν change from those of the four-state Potts universality class to Ising-like exponents close to ${\mathit{T}}_{\mathit{c}}$, a behavior qualitatively in agreement with the effect of random quenched impurities.