University of Minnesota
School of Physics & Astronomy

Condensed Matter Seminar

Thursday, October 25th 2007
1:25 pm:
Condensed Matter Seminar in 210 Physics
Speaker: Matthieu Wyart, Harvard University
Subject: Soft Modes, Rigidity and Relaxation in Amorphous Solids

We poorly understand the microscopic properties of amorphous solids, such as transport, force propagation or even the nature of their mechanical stability. These questions are related to the presence of soft modes in their vibrational spectrum. We explain the nature of these modes in repulsive, short-range systems. This enables to derive a microscopic criterion of rigidity which extends a previous result of Maxwell. This implies that rigidity is not a local property, but is characterized by a length which depends on the packing geometry, and which can be large and even diverge, e.g. near the random close packing. We argue that this description applies to granular media, silica and colloidal glasses. We propose a description of the glass transition in hard sphere systems in terms of these soft modes.
This leads to several predictions, in particular a non-trivial power law scaling characterizing the packing geometry in the glass phase, that we check numerically.

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