Quasi-equilibrium nonadditivity

TL;DR

This paper explores how short-range interacting systems can exhibit nonadditivity in quasi-equilibrium states, demonstrated through a model coupling spin and motional degrees of freedom that undergoes structural phase transitions.

Contribution

It introduces the concept of nonadditivity in quasi-equilibrium states and analyzes a specific coupled spin-motional model showing structural phase transitions.

Findings

Nonadditivity can occur in short-range systems in quasi-equilibrium.

Coupled spin and motional degrees of freedom can lead to structural phase transitions.

The paper clarifies the conditions under which nonadditivity arises in such systems.

Abstract

The possibility that a short-range interacting system exhibits nonadditivity is investigated. After the discussion on the precise definition of additivity and its consequence, we show that it is possible when the system is in a quasi-equilibrium state by examining the specific model, in which the spin degrees of freedom are coupled to the motional degrees of freedom and which exhibits a type of structural phase transitions.