The structure and spectrum of the anisotropically confined two-dimensional Yukawa system

We have studied the structural and spectral properties of the classical system consisting of a finite number of charged particles, moving in two dimensions (2D), and interacting through a screened Coulomb potential and held together by an anisotropic harmonic potential. It is known that for the bare Coulomb interaction, the system crystallizes in well defined ordered configurations in which the particles are distributed in shells. However, we have found that the occupation of the shells changes considerably as a function of the screening parameter, and for large screening, the shell structure disappears and the particles form a Wigner lattice. We have shown that the eigenmodes of the system stiffen with increasing screening. By increasing the anisotropy of the confining potential, we were able to drive the system from 2D to 1D; this change occurs through a series of structural transitions. These transitions are reflected in the mode spectrum which collapses into a narrower frequency region with increasing anisotropy.