Dynamic light scattering study of phase transitions in three-dimensional complex plasmas

The phase transitions of a three-dimensional complex (dusty) plasma under gravity are studied by means of the dynamic light scattering technique. The thermal energy of the dust component is determined during the phase transition to characterize the phase state. Detailed parametric studies are performed to examine the impact of the main plasma parameters on phase transitions. The results are found to be in good agreement with the predictions of a theoretical description of phase transitions that considers plasma instabilities to be the main heating mechanism. The distribution of energy in the system is strongly anisotropic. In the melted state, the dust particle movement in the vertical direction has much higher thermal energies than in the horizontal plane. The ratio of the two energies is constant and in particular independent of all the plasma parameters studied. Furthermore, the phase transition of the dust component is a gradual process. A transition front moves through the system in the vertical direction until the whole system reaches the new phase state. The velocities of energy fronts for the horizontal and vertical components of particle motion are very different. In particular, the melted state is a strongly inhomogeneous and anisotropic state in terms of energy transport.