Direct Estimate of the Static Length-Scale Accompanying the Glass Transition

by Dr Smarajit Karmakar (Universita di Roma, Italy)

Wednesday 28 Dec 2011, 11:00 → 12:00 Asia/Kolkata

A304 (Colaba Campus)

Glasses are liquids whose viscosity has increased so much that they cannot flow. Accordingly there have been many attempts to define a static length-scale associated with the dramatic slowing down of super-cooled liquid with decreasing temperature. In this talk, I will present a simple method to extract the desired length-scale which is highly accessible both for experiments and for numerical simulations. The fundamental new idea is that low lying vibrational frequencies come in two types, those related to elastic response and those determined by plastic instabilities. The minimal observed frequency is determined by one or the other, crossing at a typical length-scale which is growing with the approach of the glass transition. This length-scale characterizes the correlated disorder in the system: on longer length-scales the details of the disorder become irrelevant, dominated by the Debye model of elastic modes. After introducing the length-scale I will show how this scale completely determines the dynamics of the super-cooled liquid under external constraints, thereby proving beyond doubt the static nature of the proposed length-scale. Finally I talk about consequence of this scale on the mechanical properties of the amorphous solids.