Understanding aging phenomena by the free-energy-landscape approach*

Aging phenomena have been observed in many non-equilibrium systems such as polymers and glasses, where physical properties depend on the waiting time before observation. It is not known what causes the aging, nor what information can be extracted from them. Exploiting the free-energy-landscape (FEL) theory[1], which explains dynamic and thermodynamic properties of non-equilibrium systems in a unified frame work, I argue the physical origin of the aging phenomena for the first time. The FEL depends on temperature and, thus, will respond to a temperature modulation with delay. I consider physical quantities observed after a waiting time t_w when the temperature is modulated at time t = 0 and show that the delayed response of the FEL manifests itself in an additional aging. As an example, I investigate aging phenomena of dielectric relaxation represented by a two-level model. I show that the relaxation function and the linear susceptibility show non-trivial dependence on t_w from which one can deduce the relaxation time of the FEL.
[1] T. Odagaki, J. Phys. Soc. Jpn. 86, 082001(2017).