First-order transition in a three-dimensional disordered system.
We present the first detailed numerical study in three dimensions of a first-order phase transition that remains first order in the presence of quenched disorder (specifically, the ferromagnetic-paramagnetic transition of the site-diluted four states Potts model). A tricritical point, which lies surprisingly near the pure-system limit and is studied by means of finite-size scaling, separates the first-order and second-order parts of the critical line. This investigation has been made possible by a new definition of the disorder average that avoids the diverging-variance probability distributions that plague the standard approach. Entropy, rather than free energy, is the basic object in this approach that exploits a recently introduced microcanonical Monte Carlo method.
Fernández
L A
LA
Departamento de Física Teórica I, Universidad Complutense, 28040 Madrid, Spain.
Gordillo-Guerrero
A
A
Martín-Mayor
V
V
Ruiz-Lorenzo
J J
JJ