Taming Polar Active Matter with Moving Substrates: Directed Transport and Counterpropagating Macrobands

TL;DR

This paper demonstrates how moving substrates can control collective patterns in active matter, enabling directed transport and formation of macrobands that move counter to the substrate’s motion, offering new ways to manipulate active systems.

Contribution

It introduces a novel scheme to control collective behavior in active matter using traveling wave potentials, leading to macroband formation and counterpropagating transport.

Findings

Bands pin to the potential and move with it.

Collisions lead to self-organization into macrobands.

Macrobands can move against the potential's direction.

Abstract

Following the goal of using active particles as targeted cargo carriers aimed, for example, to deliver drugs towards cancer cells, the quest for the control of individual active particles with external fields is among the most explored topics in active matter. Here, we provide a scheme allowing to control collective behaviour in active matter, focusing on the fluctuating band patterns naturally occurring e.g. in the Vicsek model. We show that exposing these patterns to a travelling wave potential tames them, yet in a remarkably nontrivial way: the bands, which initially pin to the potential and comove with it, upon subsequent collisions, self-organize into a macroband, featuring a predictable transport against the direction of motion of the travelling potential. Our results provide a route to simultaneously control transport and structure, i.e. micro- versus macrophase separation, in polar active matter.