paper

Self-Averaging, Distribution of Pseudo-Critical Temperatures and Finite Size Scaling in Critical Disordered Systems

arXiv:cond-mat/9802102 · doi:10.1103/PhysRevE.58.2938

Abstract

The distributions of singular thermodynamic quantities in an ensemble of quenched random samples of linear size at the critical point are studied by Monte Carlo in two models. Our results confirm predictions of Aharony and Harris based on Renormalization group considerations. For an Ashkin-Teller model with strong but irrelevant bond randomness we find that the relative squared width, , of is weakly self averaging. , where is the specific heat exponent and is the correlation length exponent of the pure model fixed point governing the transition. For the site dilute Ising model on a cubic lattice, known to be governed by a random fixed point, we find that tends to a universal constant independent of the amount of dilution (no self averaging). However this constant is different for canonical and grand canonical disorder. We study the distribution of the pseudo-critical temperatures of the ensemble defined as the temperatures of the maximum susceptibility of each sample. We find that its variance scales as and NOT as R_χ\sim 70R_χ(T_c)χT_c(i,l)m_i(T_c,l)T_c(i,l)(T-T_c(i,l))/T_c$. This function is found to be universal and to behave similarly to pure systems.

31 pages, 17 figures, submitted to Phys. Rev. E

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