Dynamics of self-propelled particles in the vibrated dense granular media*

Living organisms and self-propelled particles self-organize into swarms and macrostructure. Reprogramming the self-organization of components provides huge opportunities to modulate structural properties and emergent functions. While structural stability requires the units to assume a solid-like state, the ability to switch target functions requires a certain degree of structural fluidity so that the units can redistribute themselves. Here, we investigate the dynamics of a small number of self-propelled particles placed among a crowd of randomly vibrated granular particles close to the jamming condition in a two-dimensional confinement. By tuning the shape and the polarity of the self-propelled particles, we can control their mobility and pathway inside the densely packed particle crowd. Our experiments and theoretical analysis show that the aspect ratio and the number of self-propelled particles determine the dynamics of the particles along the boundary. These results suggest that merely changing the particle shape and number can effectively modulate the collective motion of a self-organized structure.