Nonequilibrium phase transitions in sheared colloids

Colloidal crystals under steady shear flow are known to melt by a first order transition. At high shear rates, molecular dynamics simulations show a reentrant transition by which the system orders back into a flowing crystalline phase. We describe here a simple two variable model which captures both these phase transitions. In doing so we propose a prescription for identifying the stable phase in nonequilibrium steady states which should apply to a variety of other problems.