Structural Properties of Screened Coulomb Balls

Small three-dimensional strongly coupled charged particles in a spherical confinement potential arrange themselves in a nested shell structure. By means of experiments, computer simulations, and theoretical analysis, the sensitivity of their structural properties to the type of interparticle forces is explored. While the normalized shell radii are found to be independent of shielding, the shell occupation numbers are sensitive to screening and are quantitatively explained by an isotropic Yukawa model.

Figure 1

Radial particle distribution for $N=190$ given in cylindrical coordinates. Left: experiment 1, right two figures: MD-simulation results with Coulomb ($\kappa =0$), and Yukawa ($\kappa =1$) potential. The shell occupation numbers are compiled in Table .

Figure 2

Experimental (symbols) and MD-simulation (lines) results for the shell radii of three-dimensional Coulomb balls in units of the mean interparticle distance.

Figure 3

Experimental (symbols) and simulation (lines) results for the shell population of three-dimensional Coulomb clusters at different values of $\kappa$ (see inset).