Excluded volume causes integer and fractional plateaus in colloidal ratchet currents

TL;DR

This study demonstrates how excluded volume interactions in paramagnetic colloids driven by a rotating magnetic field lead to quantized integer and fractional ratchet currents, revealing complex collective transport phenomena.

Contribution

It introduces a detailed analysis of how excluded volume effects produce stepwise colloidal currents with integer and fractional plateaus in a magnetic ratchet system.

Findings

Current rises in quantized steps with field amplitude.

Composite clusters form due to excluded volume interactions.

Transport modes include synchronous and period-doubled hopping.

Abstract

We study the collective transport of paramagnetic colloids driven above a magnetic bubble lattice by an external rotating magnetic field. We measure a direct ratchet current which rises in integer and fractional steps with the field amplitude. The stepwise increase is caused by excluded volume interactions between the particles, which form composite clusters above the bubbles with mobile and immobile occupation sites. Transient energy minima located at the interstitials between the bubbles cause the colloids to hop from one composite cluster to the next with synchronous and period doubled modes of transport. The colloidal current may be polarized to make selective use of type up or type down interstitials.