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

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.
Comment: * Phys. Fluids, to appear (2023) * 11 pages, 8 figures. * For experiments data and movies see https://doi.org/10.5281/zenodo.5141570 * For the original angle tracking code see https://doi.org/10.5281/zenodo.7226254