Thermodynamics of the glassy state: effective temperature as an additional system parameter

TL;DR

This paper proposes a thermodynamic framework for the glassy state, introducing an effective temperature for slow configurational modes, supported by analytical solutions of a toy model.

Contribution

It presents a unifying thermodynamic description of glasses using effective temperature, linking fluctuations, susceptibilities, and fluctuation-dissipation relations.

Findings

Effective temperature describes slow modes in glasses.

Thermodynamic relations incorporate configurational entropy.

Analytical toy model supports the theoretical framework.

Abstract

A system is glassy when the observation time is much smaller than the equilibration time. A unifying thermodynamic picture of the glassy state is presented. Slow configurational modes are in quasi-equilibrium at an effective temperature. It enters thermodynamic relations with the configurational entropy as conjugate variable. Slow fluctuations contribute to susceptibilities via quasi-equilibrium relations, while there is also a configurational term. Fluctuation-dissipation relations also involve the effective temperature. Fluctuations in the energy are non-universal, however. The picture is supported by analytically solving the dynamics of a toy model.