Random self-propulsion to rotational motion of a microswimmer with inertial memory

Abstract: We study the motion of an inertial microswimmer in a non-Newtonian environment with a finite memory and present the theoretical realization of an unexpected transition from its random self-propulsion to rotational (circular or elliptical) motion. Further, the rotational motion of the swimmer is followed by spontaneous local direction reversals yet with a steady state angular diffusion. Moreover, the advent of this behaviour is observed in the oscillatory regime of the inertia-memory parameter space of the dynamics. We quantify this unconventional rotational motion of microswimmer by measuring the time evolution of direction of its instantaneous velocity or orientation. By solving the generalized Langevin model of non-Markovian dynamics of an inertial active Ornstein-Uhlenbeck particle, we show that the emergence of the rotational (circular or elliptical) trajectory is due to the presence of inertial memory in the environment or medium.