Polar swimmers induce different phases in active nematics.

Swimming bacteria in passive nematics in the form of lyotropic liquid crystals are defined as a class of active matter known as living liquid crystal in recent studies. It has also been shown that liquid crystal solutions are promising candidates for trapping and detecting bacteria. Motivated by such studies, we developed a mixed model of polar swimmers in active nematics. It is found that such a mixture is highly sensitive to the presence of polar swimmers, and shows the formation of large scale defects for relative swimmer density of the order of 0.1%. Upon increasing the density of swimmers, different phases of active nematics are found and it is observed that the system shows two phase transitions. The first phase transition is a first order transition from a quasi-long ranged ordered state to disordered active nematics with larger scale defects. On further increasing density of swimmers, the system transitions to a third phase, where swimmers form large, mutually aligned clusters. These clusters sweep the whole system like a comb in entangled hair and enforce local order in the the nematic rods. In the third phase, nematic ordering increases with an increase in the density of polar swimmers. However, due to the presence of small, unaligned stray clusters, defects in the active nematic still remain.