Solid/liquid/gaseous phase transitions in plasma crystals

We present further observations of the solid/liquid and liquid/gaseous phase transition in plasma crystals. Plasma crystal is the term used to describe the recently discovered ‘‘state’’ that a colloidal plasma may assume under certain conditions—a state which has properties resembling those of metals. During the melting transition from solid to liquid the system passes through an intermediate ‘‘flow and floe’’ stage that has not been observed in other model crystals before. It may well be that this intermediate stage is a general feature of the solid/liquid phase transition in crystals. In this case it is clearly important. The fact that this stage could be detected for the first time is a consequence of the unique properties of plasma crystals: global charge neutrality, very fast response and little damping, easy experimental control, detailed imaging, and fine time resolution of the dynamics of individual particles (‘‘atoms’’).