λ-like transition in the dynamics of ratchet gears in active bath.

To what extent the orientational order of self-propelling particles affects the dynamics of active bath-immersed ratchet devices remains unclear. We report experimental results of an inverse λ-like transition of the angular velocity of two ratchet gears in an active bath of self-propelling granular rods (SPRs) at different gear distances. The transition is caused by the phase transition in the orientational order of those SPRs located in the space between the gears. Brownian dynamics simulation of confined SPRs supports these observations. Thus, conditions for the upper bound efficiency of systems of active ratchet gears were obtained.