On melting criteria for complex plasma

The present note considers melting criteria for a plasma crystal discovered in dust plasma in 1994. Separate discussions are given to three-dimensional (3D) and two-dimensional (2D) systems. In the 3D case, melting criteria are derived based on the properties of local order in a system of microparticles. The order parameters are constructed from the cumulative distributions of the microparticle histograms as functions of various rotational invariants. The melting criteria proposed are constructed using information on microparticle positions: a few snapshots of the system that allow for the determination of particle coordinates are enough to determine the phase state of the system. It is shown that criteria obtained in this way describe well the melting and premelting of 3D complex plasma. In 2D, a system of microparticles interacting via a screened Coulomb (i.e., Debye–Hückel or Yukawa) potential is considered as an example, using molecular dynamics simulations. A number of new order parameters characterizing the melting of 2D complex plasmas are considered. The order parameters and melting criteria proposed for 2D and 3D complex plasmas can be applied to other systems as well.