The Physics & Astronomy Colloquium Series presents Harsh Mathur of Case Western Reserve University on “Mechanical Modes in Crystals and Jammed Solids: A Laboratory for Topological Defects, Gapless Edge Modes and Chaos,” on Friday, Sept. 18, at 4:10 p.m.at an Online Departmental Colloquium (Virtual link to be posted later).\

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Abstract: In the first part of this talk I will discuss the mechanical properties of two dimensional crystals like the notorious BLG (bilayer graphene). We have developed a continuum elasticity model that describes domain walls and other topological defects that have been observed in BLG and that we predict are ubiquitous in two dimensional crystals. The elasticity model also predicts gapless modes along domain walls that are analogous to the electronic edge states of topological insulators; this connection is made explicit by identifying a remarkable supersymmetry in the purely classical elasticity model.

The second part of the talk is concerned with granular materials which represent a state of matter that cannot be understood within the framework of equilibrium statistical mechanics. Granular materials can flow but when the flow becomes jammed they behave like a solid. Exploiting mechanical supersymmetry we develop a universal statistical description of the vibrational spectrum of jammed granular solids that is in good agreement with observations.