Granular chiral separation

Single helical granular particle (~5 mm), when placed in a slowly rotating tube, migrates laterally to different sides dependent on the chirality. First entrained by the rotating tube up to certain height, the particle suddenly starts to slide or roll down, during which process chiral separation is made possible as the particle only rolls at certain particle orientation and thus migrates in one direction exclusively. The intricate interplay between particle shape, which determines a critical slope of rolling, and static friction, which determines a critical slope of sliding, is found responsible for the chiral separation and its efficiency. We corroborate the experimental finding with theoretical predictions and extend the single particle phenomena to multi-particles.