Title: Emergent electromagnetism in Jammed granular solids

Speaker: Dr. Subhro Bhattacharjee, ICTS, Bangalore

Abstract: Emergence of low energy degrees of freedom is a recurrent theme in condensed matter systems. In more familiar systems such as crystalline solids the emergence of phonons as collective modes of vibration are associated mainly with broken translational symmetry that governs the physics at low temperatures. However, in a wide class of systems, local energetic constraints may take the form of Gauss's law giving rise to an emergent electromagnetism at low energies. In this talk, I shall start with a brief review of such emergent electromagnetism in discussing their basic features as well as the general settings in which they appear. Then I shall apply it to understand the mechanical response of naturally abundant granular solids such as sand grains where local conditions of mechanical equilibrium, i.e., force and torque balance on each grain, as I shall show, have the mathematical structure of a generalized Gauss's law for a rank-2 U(1) electromagnetism. The electrostatic limit of this tensor electromagnetism successfully captures the anisotropic "elasticity" of granular solids and provides a new framework to understand a large class of such systems.