Fernández Pérez, Luis AntonioGordillo Guerrero, A.Martín Mayor, VíctorRuiz Lorenzo, J. J.2023-06-202023-06-202008-02-080031-900710.1103/PhysRevLett.100.057201https://hdl.handle.net/20.500.14352/51915© 2008 American Physical Society. This work has been partially supported by MEC through Contracts No. FIS2004-01399, No. FIS2006-08533-C03, No. FIS2007-60977 and by CAM and BSCH. Computer time was obtained at BIFI, UCM, UEX, and, mainly, in the Mare Nostrum. The authors thankfully acknowledge the computer resources and technical expertise provided by the Barcelona Supercomputing Center.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.engjournal articlehttp://doi.org/10.1103/PhysRevLett.100.057201http://journals.aps.org/open access5351-73Diluted ising-modelBond Potts modelsCritical-behaviorPhase-transitionsMonte-CarloCritical exponents.Física (Física)Física-Modelos matemáticos22 Física