Topological defects lead to energy transfer in active nematics

Abstract: Active nematics are fluids in which the components have nematic symmetry and are driven out of equilibrium due to the microscopic generation of an active stress. When the active stress is high, it drives flows in the nematic and can lead to the proliferation of topological defects, a state we refer to as defect chaos. Using numerical simulations of active nematics, we observe energy transfer between length scales during defect chaos. We demonstrate that this energy transfer is driven by the exchange between variations in the orientation and degree of order in the nematic that predominantly occur during defect creation and annihilation. We then show that the primary features of energy transfer during defect chaos scale with the active length scale. Finally, we identify a second regime that features few defects, but rather bend walls. Similar to topological defects, these bend walls co-localize variations in the orientation with variations in the scalar order parameter leading to energy transfer.