Kinetics of phase transitions in the presence of an intermediate metastable state: a generic model

The role of an intermediate metastable state in the fluctuation-induced transitions between two stable states is analyzed using generic kinetic models involving one and two order parameters. Conditions are identified under which the transition rate can be enhanced by the presence of the intermediate state. The relevance of the results in the crystallization of materials such as protein solutions, in which the attractive part of interparticle interactions is weak and short ranged, is discussed.