Physics Department - The Beauty of Being Broken: Order, Disorder, and Defects in Complex Matter

Abstract
Physics has a long-standing love affair with symmetry and order. Yet in real materials, perfection is often not where the interesting physics happens.  It is the imperfections—the defects—that control phenomena ranging from the plastic deformation of solids to the melting of two-dimensional materials.  However, a defect is normally defined as something that disrupts an underlying order. So what is a defect when that order is hidden, approximate, or dynamical?  In this talk, I will explore how the idea of defects can be pushed beyond its traditional setting. We will first see how generalized topological defects can emerge in amorphous solids and provide a new way of thinking about how glasses lose rigidity. We will then ask how defects form when a sharp phase transition is replaced by a crossover. Finally, we will venture into systems with order in space and time, where defects acquire unusual dynamics and roles far from equilibrium.  The broader message is that, in complex matter, defects are often not merely imperfections, but the key to understanding the physics.