Direct manipulation of diffusion in colloidal glasses via controlled generation of quasi-particle-like defects.

We experimentally manipulate the structural relaxation of colloidal glass at an atomistically controlled position. We focus a laser beam to eject a particle from the colloidal system. This creates a void that transforms rapidly into a mobile soft spot (quasivoid) composed of a few neighboring free-volume fragments. The transformation and subsequent motions of the quasivoid trigger a sequence of well-connected stringlike motions emanating precisely from the point of laser action with free volumes flowing along the string. Furthermore, the sequence can be terminated by the annihilation of the quasivoid. The observations are supported by molecular dynamics (MD) simulations.