Session LC42 - Phase Transitions and Critical Phenomena.
ORAL session, Tuesday afternoon, March 23
Knollwood Room A, Omni Hotel
Motivated by recent experiments on phase behavior of systems confined in porous media, we have studied the effect of randomness on the nature of the phase transition in the two dimensional Potts model. To model the effects of the porous matrix we introduce a random distribution of couplings, \cal P (J_ij)=p\delta (J_ij-J_1)+(1-p)\delta (J_ij-J_2), in the q state Potts Hamiltonian. An extensive Monte Carlo study is made on this system for q=5. We studied two different cases of disorder (a) J_1/J_2\to \infty and p=0.8 and (b) J_1/J_2=10 and p=0.5. We observed, in both cases, that the weak first order transition that appears in the pure case, changes two a second order transition. A finite size scaling analysis shows that, the correlation length exponent, \nu is close to 1 and the best fit to the dependence of the specific heat on system size is logarithmic. This suggests that both cases belong to the universality class of the Ising model. In contrast, the magnetic exponents point to a different universality class.