Activity induced trapping in a saw-tooth ratchet potential

TL;DR

This paper investigates how active particles in a saw-tooth ratchet potential exhibit activity-induced trapping, with transport properties influenced by activity persistence, particle mass, and medium viscosity, revealing transitions and optimization possibilities.

Contribution

It introduces a comprehensive analysis of inertial active particles in ratchet potentials, highlighting activity-induced transitions and the effects of persistence time and mass on transport and coherence.

Findings

Transport is directed by spatial asymmetry.

Particle trapping occurs with increased activity persistence.

Transport coherence can be optimized by tuning activity duration.

Abstract

We consider an inertial active Ornstein-Uhlenbeck particle self-propelling in a saw-tooth ratchet potential. Using the Langevin simulation and matrix continued fraction method, the particle transport, steady state diffusion, and coherence in transport are investigated throughout the ratchet. Spatial asymmetry is found to be the key criterion for the possibility of directed transport in the ratchet. Interestingly, the simulated particle trajectories and the corresponding position and velocity distribution functions reveal that the system passes through an activity-induced transition in the transport from the running phase to the locked phase with the self-propulsion/activity time of the dynamics. This is further corroborated by the mean square displacement (MSD) calculation. The MSD gets suppressed with increase in the persistence of activity in the medium and finally approaches zero for very large value of self propulsion time, reflecting a kind of trapping of the particle by the ratchet for longer persistent of activity in the medium. The non-monotonic behaviour of the particle current and Peclet number with self propulsion time confirms that the particle transport and it's coherence can be enhanced or reduced by fine tuning the persistent duration of activity. Moreover, for an intermediate range of self-propulsion time in the dynamics as well as for an intermediate range of mass of the particle, even though the particle current shows a pronounced unusual maximum with mass, there is no enhancement in the Peclet number, instead the Peclet number decreases with mass, confirming the degradation of coherence in transport. Finally, from the analytical calculations, it is observed that for a highly viscous medium, where the inertial influence is negligibly small, the particle current approaches the current in the over damped regime.