Brownian magneto-gyrator as a tunable microengine

Abstract

A Brownian particle performs gyrating motion around a potential energy minimum when subjected to thermal noises from two different heat baths. Here, we propose a magneto-gyrator made of a single charged Brownian particle that is steered by an external magnetic field. Key properties, such as the direction of gyration, the torque exerted by the engine on the confining potential and the maximum power delivered by the microengine can be tuned by varying the strength and direction of the applied magnetic field. Further tunability is obtained by rotating the potential in the plane perpendicular to the direction of the magnetic filed. We show that in this generic scenario, the microengine can be stalled and even reversed by the magnetic field. Finally, we highlight a property of the magneto-gyrator that has no counterpart in the overdamped approximation-the heat loss from the hot to cold bath requires explicit knowledge of the mass of the particle. Consequently, the efficiency of the microengine is mass-dependent even in the overdamped limit.

Escape dynamics in an anisotropically driven Brownian magneto-system

“…We assume that the barrier height ΔE = 1 2 ka 2 , is sufficiently large that the particle leaks out slowly across the trap and settles into a quasistationary state: the escape is a Poisson process with the inverse rate of mean escape time t esc . The quasistationary probability density is given by P (r, t) ∼ ρ ss (r)e −t/ tesc where ρ ss (r) is the steadystate probability density obtained in the limit of a → ∞ which we have obtained in previous works [25,26] and in the SM. The total outgoing flux at r = a is given by J(t) = − d dt 2π 0 a 0 P (r, θ, t)rdrdθ where P (r, θ, t) is the quasistationary probability distribution in the polar coordinates.…”

“…In contrast, in an anisotropically driven system, a magnetic field affects the dynamics in a qualitatively different way [25]. While curving the trajectory of a particle, there also occurs energy transfer in form of heat from the hot source to the cold source, which is mediated by the magnetic field [26]. As a consequence, at large magnetic fields, the two spatial degrees of freedom become identical regardless of the difference between noise strengths.…”

“…In future work we aim to extend our model to the escape through a narrow hole [35][36][37]. An interesting generalization would be to replace the isotropic potential by an anisotropic potential where the stationary state of the system is characterized by not only a non-Boltzmann probability distribution, but also additional Lorentz fluxes [26]. Also, it could be interesting to study the escape in an anisotropically driven Brownian magneto-system from a bistable state, which might be realized by trapping the particle using two optical tweezers [38].…”

Active chiral molecules in activity gradients

“…ian particles also perform odd-diffusive motion under the effect of the Lorentz force [29][30][31][32][33]. While active chiral particles rotate due to the microscopic active torque, in the case of charged particles under magnetic field a certain handedness is introduced by the Lorentz force.…”