Bond Orientational Order Parameters in the Crystalline Phases of the   Classical Yukawa-Wigner Bilayers
  We present a study of the structural properties of the crystalline phases for a planar bilayer of particles interacting via repulsive Yukawa potentials in the weak screening region. The study is done with Monte Carlo computations and the long ranged contributions to energy are taken into account with the Ewald method for quasi-two dimensional systems. Two first order phase transitions (fluid-solid and solid-solid) and one second order transition (solid-solid) are found when the surface density is varied at constant temperature. A particular attention is pay to the characteristics of the crystalline phases by the analysis of bond orientational order parameters and center-to-center correlations functions. 
Martial Mazars (Laboratoire de Physique Theorique - UMR 8627 /   Universite Paris-Sud / Orsay / FRANCE)