ICTS

Topological defects play a prominent role in the physics of two-dimensional materials. In active nematics, which are orientationally ordered fluids composed of self-driven elongated particles, disclinations can acquire spontaneous self-propulsion and drive self-sustained flows upon proliferation. Here, I present a comprehensive theory of active nematics by recognizing that defects are the relevant excitations in the system. Upon extending the well-known Coulomb gas mapping of equilibrium defects to the active realm, we develop an effective particle like description of interacting active defects. Using this, we demonstrate that activity drives a nonequilibrium defect unbinding transition to active turbulence, which can further transition to a novel defect ordered flock at high activity. Furthermore, within a hydrodynamic approach, we also show that spatially inhomogeneous activity can be used to pattern and segregate defects, demonstrating the versatility and relevance of our framework to control and design transport in active metamaterials and devices.