Emergent dynamics of large scale collective rotations in 2D active nematic

Motivated by recent work on active nematics we employ here a microtubule and kinesin motor gliding assay system to examine dynamic collective order in 2D. Without the need for a depletion agent, our system exhibits the classic nematic order transition that depends on microtubule and active motor density. However in the regime of very flexible microtubules nematic order is lost, suggesting that this ordering is a consequence of both microtubule stiffness and density. We demonstrate that the ordered state exhibts large scale coherent rotations and that the introduction of a time varying director is necessary for proper characterization of the active nematic system. We show that the rate of this collective rotation of the nematic order is strongly dependent on activity induced microtubule fluctuations.