Viscoelastic response of an active particle under the action of magnetic field

TL;DR

This study investigates the complex viscoelastic response of an active charged particle under magnetic fields, revealing re-entrant active-passive behavior and the influence of elastic dissipation and activity timescales.

Contribution

It provides an exact analytical and numerical analysis of active particle dynamics in viscoelastic media under magnetic fields, highlighting novel re-entrant transition phenomena.

Findings

MSD shows enhancement or suppression depending on activity and dissipation timescales.

Strong magnetic fields cause the particle to behave like an inert passive Brownian particle.

For free particles, displacement always decreases with increasing magnetic field.

Abstract

We consider the dynamics of a charged inertial active Ornstein-Uhlenbeck particle in a viscoelastic suspension under the action of an uniform magnetic field. With the help of both numerical simulation and analytical framework, we exactly investigate the viscoelastic response of the particle to the magnetic field by means of particle trajectories, mean displacement, and mean square displacement (MSD) calculations. The simulated particle trajectories and MSD calculations reveal that the steady state response of a confined harmonic particle to the magnetic field show interesting features due to the complex interplay of underlying physical processes such as elastic dissipation and active fluctuations in the medium. When the activity time scale of the dynamics is larger than the elastic dissipation timescale (or vice-versa), the steady state MSD shows an enhancement (or suppression) with increase in the field strength. In both the cases, for very strong magnetic field the MSD interestingly approaches the value at the equilibrium limit where the generalized fluctuation dissipation relation is satisfied and the particle behaves like an inertial passive Brownian particle. Thus, for a finite magnetic field, the system exhibits a re-entrant type transition from active to passive and then to active behaviour with persistence of elastic dissipation in the medium. However, for a free particle, the overall displacement covered always gets suppressed with increase in the strength of the magnetic field and finally approaches zero for a very strong magnetic field.