Collective modes in 2-D Yukawa solids and liquids

We report comparative studies on collective excitations in 2-D complex plasmas, in which particles interact through the Yukawa potential, encompassing both the solid and the strongly coupled liquid states. Dispersion and polarization of the collective modes in the solid state are calculated through the lattice summations, while in the liquid state, through molecular dynamics (MD) simulations in conjunction with the theoretical quasi-localized charge approximation analysis. The latter closely emulates the dispersion, resulting from an angular averaging in the lattice. In general, however, the lattice dispersion is substantially different from that of the liquid. The MD simulations show the dramatic transformation of the anisotropic phonon dispersion of the crystal lattice near the solid4iquid transition into the isotropic liquid dispersion.