First order transition in a three dimensional disordered system

TL;DR

This paper numerically investigates a first-order phase transition in a three-dimensional disordered system, revealing a tricritical point near the pure system limit using a novel disorder averaging method and microcanonical Monte Carlo.

Contribution

It introduces a new disorder averaging technique and applies it to study the first-order transition in a 3D disordered system, identifying a tricritical point.

Findings

First-order transition persists in 3D disordered system.

A tricritical point is located near the pure system limit.

A new disorder averaging method improves analysis.

Abstract

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 to 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.