Self-organized criticality in sheared suspensions.

Recent studies reveal that suspensions of neutrally buoyant non-brownian particles driven by slow periodic shear can undergo a dynamical phase transition between a fluctuating irreversible steady state and an absorbing reversible state. Using a computer model, we show that such systems exhibit self-organized criticality when a finite particle sedimentation velocity v(s) is introduced. Under periodic shear, these systems evolve, without external intervention, towards the shear-dependent critical concentration phi(c) as v(s) is reduced. This state is characterized by power-law distributions in the lifetime and size of fluctuating clusters. Experiments exhibit similar behavior and, as v(s) is reduced, yield steady-state values of phi that tend towards the phi(c) corresponding to the applied shear.