Hardcore Run and Tumble Particles with Time-Periodic Drive

Abstract

We consider a set of hardcore run and tumble particles on a 1d periodic lattice. The effect of external potential has been modeled as a special site where the tumbling probability is much larger than the rest of the system. We call it a ‘defect’ site and move its location along the ring lattice with speed u. When bulk tumbling rate is zero, in absence of any defect the system goes to a jammed state with no long range order. But introduction of the moving defect creates a strongly phase separated state where almost all active particles are present in a single large cluster, for small and moderate u. This striking effect is caused by the long-ranged velocity correlation of the active particles, induced by the moving defect. For large u, a single large cluster is no longer stable and breaks into multiple smaller clusters. When bulk tumbling rate is non-zero, a competition develops between the time-scales associated with tumbling and defect motion. While the moving defect attempts to create long ranged velocity order, bulk tumbling tends to randomize the velocity alignment. If the bulk tumbling rate is small enough such that relatively small number of tumbles take place during the time the moving defect travels through the entire system, the defect has enough time to restore the order in the system and our simulations show that the long range order in velocity and density survive. For larger tumbling rate, long range order is destroyed and the system develops multiple regions of high density and low density regions. We also propose possible experimental setup where our results can be verified.