Glassy aging with modified Kohlrausch-Williams-Watts form

Abstract

In this paper, we address the question of whether aging in the nonequilibrium glassy state is controlled by the equilibrium a-relaxation process, which occurs at temperatures above T_g. Recently, Lunkenheimer et al. [Phys. Rev. Lett. 95, 055702 (2005)] proposed a model for the glassy aging data of dielectric relaxation using a modified Kohlrausch-Williams-Watts form exp[-(t_age/τ_age)β_age]. The aging time t_age dependence of the relaxation time τ_age is defined by these authors through a functional relation involving the corresponding frequency v(t_age)=1/(2π τ_age), but the stretching exponent β_age is the same as β_α , the α-relaxation stretching exponent. We present here an alternative functional form for τ_age(t_age) directly involving the relaxation time itself. The proposed model fits the data of Lunkenheimer et al. perfectly with a stretching exponent β_age different from β _α.