Absolute negative mobility of an active tracer in a crowded environment

TL;DR

This paper develops a microscopic theory explaining absolute negative mobility (ANM) of an active tracer in crowded environments, revealing the conditions and mechanisms behind this counterintuitive transport phenomenon.

Contribution

It introduces a detailed analytical model for ANM in active tracers on a lattice with crowders, linking microscopic parameters to the emergence of ANM.

Findings

ANM occurs under specific parameter ranges.

The environment's response influences ANM.

ANM is related to negative differential mobility.

Abstract

Absolute negative mobility (ANM) refers to the situation where the average velocity of a driven tracer is opposite to the direction of the driving force. This effect was evidenced in different models of nonequilibrium transport in complex environments, whose description remains effective. Here, we provide a microscopic theory for this phenomenon. We show that it emerges in the model of an active tracer particle submitted to an external force, and evolving on a discrete lattice populated with mobile passive crowders. Resorting to a decoupling approximation, we compute analytically the velocity of the tracer particle as a function of the different parameters of the system, and confront our results to numerical simulations. We determine the range of parameters where ANM can be observed, characterize the response of the environment to the displacement of the tracer, and clarify the mechanism underlying ANM and its relationship with negative differential mobility (another hallmark of driven systems far from the linear response).