Lagrangian phase transitions in nonequilibrium thermodynamic systems

TL;DR

This paper investigates phase transitions in nonequilibrium thermodynamic systems, revealing that the nonequilibrium free energy functional can exhibit singularities, unlike the convex equilibrium case, with a focus on a specific exclusion process.

Contribution

It introduces the concept of Lagrangian phase transitions in nonequilibrium systems and analyzes their occurrence in a boundary driven exclusion process.

Findings

Identification of non-convex free energy functionals in nonequilibrium

Discovery of phase transition singularities in specific exclusion processes

Conditions under which phase transitions occur in driven systems

Abstract

In previous papers we have introduced a natural nonequilibrium free energy by considering the functional describing the large fluctuations of stationary nonequilibrium states. While in equilibrium this functional is always convex, in nonequilibrium this is not necessarily the case. We show that in nonequilibrium a new type of singularities can appear that are interpreted as phase transitions. In particular, this phenomenon occurs for the one-dimensional boundary driven weakly asymmetric exclusion process when the drift due to the external field is opposite to the one due to the external reservoirs, and strong enough.