Bona Fide Thermodynamic Temperature in Nonequilibrium Kinetic Ising Models

TL;DR

This paper demonstrates that a consistent and unique thermodynamic temperature can be defined across the phase diagram of certain nonequilibrium kinetic Ising models, revealing universal amplitude ratios at critical points.

Contribution

It introduces a method to define a bona fide temperature in nonequilibrium kinetic Ising models and confirms the universality of fluctuation-dissipation ratios at criticality.

Findings

Nominal temperature is well-defined throughout the phase diagram.

Universal fluctuation-dissipation ratio $X_ $ at critical points.

Values of $X_ $ for different universality classes.

Abstract

We show that a nominal temperature can be consistently and uniquely defined everywhere in the phase diagram of large classes of nonequilibrium kinetic Ising spin models. In addition, we confirm the recent proposal that, at critical points, the large-time ``fluctuation-dissipation ratio'' $X_\infty$ is a universal amplitude ratio and find in particular $X_\infty \approx 0.33(2)$ and $X_\infty = 1/2$ for the magnetization in, respectively, the two-dimensional Ising and voter universality classes.