Abstract

In recent years, delayed feedback in colloidal systems has become an active and promising field of study in theory [1] and experiments [2,3], key topics being history dependence and the manipulation of transport properties. Based on Brownian dynamics simulations we here study the collective behavior [4] of a two-dimensional system of repulsively interacting colloidal particles, where each particle is propelled [5] by a non-linear, time-delayed repulsive feedback force with time delay τ. We first observe and quantify the emergence of dynamical clustering and spontaneous velocity alignment leading to collective motion characterized by a non-zero mean velocity. We then provide an explanation for the underlying mechanism of local velocity alignment, combining single-particle and mean-field-like effects. Finally, we introduce a length scale based argument to explain the global spreading of alignment information in our system, revealing similarities to Vicsek-like models. [1] S. A. M. Loos, and S. H. L. Klapp, Scientific Reports 9, 2491 (2019) [2] M. A. Fernandez-Rodriguez et al., Nature Communications 11, 4223 (2020) [3] Bell-Davies M. C. R., Curran A., Liu Y. and Dullens R. P. A., Phys. Rev. E 107 , 064601 (2023) [4] R. A. Kopp and S. H. L Klapp, EPL 143 , 17002 (2023) [5] R. A. Kopp and S. H. L Klapp, Phys. Rev. E 107 , 024611 (2023)