Frequency-domain study of physical aging in a simple liquid

We characterize the time dependence of the frequency-dependent dielectric susceptibility of glycerol following quenches to low temperature. For quenches to temperatures not far below the glass-transition temperature, the spectral shape and position during equilibration closely approximate those of equilibrium spectra at higher temperatures. For deeper quenches the correspondence with equilibrium spectra breaks down, and we observe more subtle behavior. Most of the susceptibility's change with time occurs within one equilibrium relaxation time after the quench, and our results do not support the presence of a significant ultraslow component to the equilibration of the dielectric response. We find some qualitative agreement between the time dependence of the susceptibility and analogous measurements on spin glasses; however, closer inspection reveals that the liquid fails to reproduce many of the salient features of the spin-glass behavior.