Universal behavior of relaxational heterogeneity in glasses and liquids
D. Caprion, J. Matsui, H. R. Schober
Abstract
We report an investigation of the heterogeneity in super-cooled liquids and glasses using the non-Gaussianity parameter. We simulate selenium and a binary Lennard-Jones system by molecular dynamics. In the non-Gaussianity three time domains can be distinguished. First there is an increase on the ps-scale due to the vibrational (ballistic) motion of the atoms. This is followed, on an intermediate time-scale, by a growth, due to local relaxations (beta-relaxation) at not too high temperatures. A maximum is reached at times corresponding to long range diffusion (alpha-relaxation). At long times the non-Gaussianity slowly drops, the system becoming homogeneous on these time-scales. In both systems studied, the non-Gaussianity follows in the intermediate time domain, corresponding to the beta-relaxations, a law ~ t1/2. This general behavior is explained by collective hopping and dynamic heterogeneity. We support this finding by a model calculation.
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