title: Dislocation reactions, grain boundaries, and irreversibility in two-dimensional lattices using topological tweezers.
abstract: Dislocations, disclinations, and grain boundaries are topological excitations of crystals that play a key role in determining out-of-equilibrium material properties. In this article we study the kinetics, creation, and annihilation processes of these defects in a controllable way by applying "topological tweezers," an array of weak optical tweezers which strain the lattice by weakly pulling on a collection of particles without grabbing them individually. We use topological tweezers to deterministically control individual dislocations and grain boundaries, and reversibly create and destroy dislocation pairs in a 2D crystal of charged colloids. Starting from a perfect lattice, we exert a torque on a finite region and follow the complete step-by-step creation of a disoriented grain, from the creation of dislocation pairs through their reactions to form a grain boundary and their reduction of elastic energy. However, when the grain is rotated back to its original orientation the dislocation reactions do not retrace. Rather, the process is irreversible; the grain boundary expands instead of collapsing.
authors.affiliation: Physics Department and James Franck Institute, The University of Chicago, Chicago, IL 60605.
authors.forename: William T M
authors.initials: WT
authors.lastname: Irvine
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Hollingsworth
authors.forename: David G
authors.initials: DG
authors.lastname: Grier
authors.forename: Paul M
authors.initials: PM
authors.lastname: Chaikin
keywords: colloidal crystal; holographic trapping; topological defect