Anisotropic plasma cyrstals: Phase diagram

Summary form only given. Laboratory complex (dusty) plasmas are low-pressure gas- discharge plasmas containing monodisperse microparticles that are highly charged due to absorption of ambient electrons and ions. The unique feature distinguishing complex plasmas is that one can vary the strength of the electrostatic coupling between particles over an extremely broad range. This allows us to explore the entire hierarchy of the phase states - ranging from gaseous to solid - and thus study all relevant generic processes occurring in strongly coupled media at the most fundamental kinetic level. Recently, the experimental discovery of "electrorheological" complex plasmas has been reported1. In such plasmas the interaction between microparticles can be controlled by external AC electric fields, due to distortion of the Debye spheres that surround microparticles. We show that interactions in electrorheological complex plasmas are equivalent to those in conventional dipolar fluids. Results of the recent microgravity experiments and complementary molecular dynamics simulations reveal variety of phase transitions controlled by the amplitude of the field, resulting in different anisotropic ("string-like") solid structures. We also report on a comprehensive thermodynamic study of anisotropic complex plasmas (with a spherically-symmetric repulsive Yukawa interaction and additional dipole-dipole interaction) induced by an external field. We propose a simple variational approach based on the Bogoliubov inequality for determining equilibrium solid phases. We show that the phase diagram of such complex plasmas exhibits numerous solid-solid phase transitions precisely controlled by the magnitude of the applied field.