title: Relaxation mechanisms in glassy dynamics: the Arrhenius and fragile regimes.
abstract: Generic glass formers exhibit at least two characteristic changes in their relaxation behavior, first to an Arrhenius-type relaxation at some characteristic temperature and then at a lower characteristic temperature to a super-Arrhenius (fragile) behavior. We address these transitions by studying the statistics of free energy barriers for different systems at different temperatures and space dimensions. We present a clear evidence for changes in the dynamical behavior at the transition to Arrhenius and then to a super-Arrhenius behavior. A simple model is presented, based on the idea of competition between single-particle and cooperative dynamics. We argue that Arrhenius behavior can take place as long as there is enough free volume for the completion of a simple T1 relaxation process. Once free volume is absent one needs a cooperative mechanism to "collect" enough free volume. We show that this model captures all the qualitative behavior observed in simulations throughout the considered temperature range.
authors.affiliation: Department of Chemical Physics, The Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: H George E
authors.initials: HG
authors.lastname: Hentschel
authors.forename: Smarajit
authors.initials: S
authors.lastname: Karmakar
authors.forename: Itamar
authors.initials: I
authors.lastname: Procaccia
authors.forename: Jacques
authors.initials: J
authors.lastname: Zylberg
mesh_terms: D003198:Computer Simulation; D005898:Glass / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D044367:Phase Transition