Spin and velocity correlations in a confined two-dimensional fluid of disk-shaped active rotors

TL;DR

This study investigates velocity autocorrelations in confined two-dimensional active rotors, revealing how rotational activity influences oscillations and spin correlations, indicating emergent chirality in particle dynamics.

Contribution

It provides experimental insights into how rotational activity affects velocity autocorrelations and spin fluctuations, highlighting the emergence of chirality in active rotor systems.

Findings

Persistent small-scale oscillations in velocity autocorrelations

Large scale spin fluctuations vanish at high rotational activity

Spin correlations become anti-correlated at longer times with high activity

Abstract

We study the velocity autocorrelations in an experimental configuration of confined two-dimensional active rotors (disks). We report persistent small scale oscillations in both rotational and translational velocity autocorrelations, with their characteristic frequency increasing as rotational activity increases. While these small oscillations are qualitatively similar in all experiments, we found that, at strong particle rotational activity, the large scale particle spin fluctuations tend to vanish, with the small oscillations around zero persisting in this case, and spins remain predominantly and strongly anti-correlated at longer times. For weaker rotational activity, however, spin fluctuations become increasingly larger and angular velocities remain de-correlated at longer times. We discuss in detail how the autocorrelation oscillations are related to the rotational activity and why this feature is generically a signal of the emergence of chirality in the dynamics of a particulate system.