Emergent ordering of microswimmers in smectic liquid crystals

Self-propelled agents can interact in many different ways, including by perturbing a shared physical environment, e.g, hydrodynamic interactions. We study motile particles that are embedded into a smectic liquid crystal, locally distorting the smectic layer spacing. This results in interactions mediated by a smectic liquid crystal distortion field and corresponds to a form of “active smectic” liquid crystal. We identify several dynamical phases that emerge in different regimes of the smectic stiffness and particle reorientation time. We characterise these as (i) ballistic motion, (ii) clustering and (iii) collective motion where orientational order emerges even thought the system lacks explicit co-alignment. We further identify an order-to-disorder transition on the addition of angular noise.