Stability and dynamical properties of a double-layer Wigner crystal in two dimensions

We investigate the zero-temperature phase diagram and melting transition of a two-dimensional Wigner crystal (WC) of classical Coulombic particles in a double-layer structure. In contrast with the single-layer WC, we find that five different crystalline phases are stable in different ranges of inter-layer distance/particle density. Phase boundaries consist of both continuous and discontinuous transitions. From the phonon frequencies of the system we evaluate the melting temperature of the WC. We suggest the possibility of structural phase transitions as a function of temperature.