Structure and phase diagram of strongly-coupled bipolar charged-particle bilayers

We report Monte Carlo simulations of a classical, strongly-coupled charged-particle bilayer with opposite charges in the two layers. At layer separations comparable to the Wigner-Seitz radius the two layers support each other to establish a quasi-long- range order; at low layer separations stable dipoles (classical equivalents of bound excitons) are formed and the long-range order is extinguished as the Coulomb interaction changes to a dipole-dipole interaction. We identify dipole-liquid, dipole-solid, Coulomb-liquid and Coulomb-solid phases, which are exhibited in an intuitive phase diagram of the system in the Gamma (coupling)-d (layer separation) plane.