Kinetic heterogeneities at dynamical crossovers

Department of Physics and Astronomy, University of Pennsylvania - Philadelphia, PA 19104, USA

tom.haxton@gmail.com

Received: 2 February 2010
Accepted: 10 June 2010

Abstract

We perform molecular dynamics simulations of a model glass-forming liquid to measure the size of kinetic heterogeneities, using a dynamic susceptibility χ_ss(a, t) that quantifies the number of particles whose dynamics are correlated on the length scale a and time scale t. By measuring χ_ss(a, t) as a function of both a and t, we locate local maxima χ^⋆ at distances a^⋆ and times t^⋆. Near the dynamical glass transition, we find two types of maxima, both correlated with crossovers in the dynamical behavior: a smaller maximum corresponding to the crossover from ballistic to sub-diffusive motion, and a larger maximum corresponding to the crossover from sub-diffusive to diffusive motion. Our results indicate that kinetic heterogeneities are not necessarily signatures of an impending glass or jamming transition.