Giant increase of diffusion by small rise of friction

TL;DR

This paper shows that increasing friction can dramatically boost diffusion in a specific physical system, contrary to the usual expectation.

Contribution

The study reveals a novel mechanism where diffusion increases significantly with friction due to bifurcations in particle orbits.

Findings

Diffusion can increase by up to five orders of magnitude when friction doubles in a strong dissipation regime.

The effect is caused by bifurcations of periodic orbits and their displacement with increased friction.

In weak dissipation, diffusion increases less due to non-monotonic changes in orbit populations.

Abstract

Diffusion coefficient usually decreases when friction increases. We analyze the opposite behavior in the paradigmatic system consisting of an inertial Brownian particle moving in a symmetric spatially periodic potential and driven by an unbiased time periodic force. For tailored parameter set in strong dissipation regime the particle spreading can be giantly amplified: if the friction is twice as large then the diffusion grows up to five orders of magnitude. The mechanism lying behind this effect is related to bifurcation of periodic orbits oscillating around the potential maximum and their symmetric displacement towards the adjacent potential minima when the friction coefficient increases. On the other hand, in the weak dissipation regime, where the increase of diffusion vs friction is also observed, the effect is induced by a non-monotonic change of population of the running orbits. However, in this regime the enhancement of diffusion is much smaller.

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