title: Critical and tricritical singularities of the three-dimensional random-bond Potts model for large.
abstract: We study the effect of varying strength delta of bond randomness on the phase transition of the three-dimensional Potts model for large q. The cooperative behavior of the system is determined by large correlated domains in which the spins point in the same direction. These domains have a finite extent in the disordered phase. In the ordered phase there is a percolating cluster of correlated spins. For a sufficiently large disorder delta>deltat this percolating cluster coexists with a percolating cluster of noncorrelated spins. Such a coexistence is only possible in more than two dimensions. We argue and check numerically that deltat is the tricritical disorder, which separates the first- and second-order transition regimes. The tricritical exponents are estimated as betat/vt=0.10(2) and vt=0.67(4). We claim these exponents are q independent for sufficiently large q. In the second-order transition regime the critical exponents betat/vt=0.60(2) and vt=0.73(1) are independent of the strength of disorder.
authors.affiliation: Dipartimento di Fisica "E.R. Caianiello" and Istituto Nazionale per la Fisica della Materia, Università degli Studi di Salerno, Baronissi, Salerno I-84081, Italy.
authors.forename: M T
authors.initials: MT
authors.lastname: Mercaldo
authors.forename: J-Ch
authors.initials: JC
authors.lastname: Anglès d'Auriac
authors.forename: F
authors.initials: F
authors.lastname: Iglói