Onset of slow dynamics in dense suspensions of active colloids

Slow relaxation and heterogeneous dynamics are characteristic features of glasses. The presence of glassy dynamics in nonequilibrium systems, such as active matter, is of significant interest due to its implications for living systems and material science. In this study, we use dense suspensions of self-propelled Janus particles moving on a substrate to investigate the onset of slow dynamics. Our findings show that dense active suspensions exhibit several hallmark features of slow dynamics similar to systems approaching equilibrium. The relaxation time fits well with the Vogel-Fulcher-Tamman (VFT) equation, and the system displays heterogeneous dynamics. Furthermore, increasing the activity leads to faster relaxation of the system, and the glass transition density predicted by the VFT equation shifts to higher densities. The measurement of the cage length and persistence length reveal they are of the same order over the range of activities explored in our study. These results are in agreement with recent particle simulations.