Collective motion of vibrated polar disks

Phys Rev Lett. 2010 Aug 27;105(9):098001. doi: 10.1103/PhysRevLett.105.098001. Epub 2010 Aug 23.

Abstract

We experimentally study a monolayer of vibrated disks with a built-in polar asymmetry which enables them to move quasibalistically on a large persistence length. Alignment occurs during collisions as a result of self-propulsion and hard core repulsion. Varying the amplitude of the vibration, we observe the onset of large-scale collective motion and the existence of giant number fluctuations with a scaling exponent in agreement with the predicted theoretical value.