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François Sausset: „Characterizing order in amorphous systems”
LPTMS, Université d'Orsay, France

Is the dramatic viscous slowing down encountered in glassy systems associated with the growth of some static amorphous order? This fundamental question remains unanswered for two main reasons: First, the nature of the hypothetical order has not been firmly established, and second, the experimental implementation of the various proposals is unclear.

Recently, a generic method to define and quantify order has been proposed. Roughly, it consists of measuring the configurational entropy of patches (local clusters of varying size) in the system, and studying its scaling with patch volume V. For small patches, this patch entropy is expected to grow sub-linearly in V, while for large clusters, it grows linearly. This crossover enables us to define and measure a correlation length with no a-priori knowledge of the order involved.

We will discuss the implementation of this new proposal on atomic models of glass forming liquids and colloidal systems. As a benchmark, we will study a well-characterized numerical model of a glass forming liquid, and will compare various proposed measures, including bond-orientation and point-to-set correlation lengths.

This new method can also be used to access the symmetries of the local order, without any a priori knowledge of it. For this model the hexagonal order is, as expected, recovered. We will also show first applications to experimental data (3D colloidal systems) allowing to access both order extension and symmetries.