Anisotropic dust lattice modes

Dust lattice (DL) wave modes in a one-dimensional plasma crystal suspended in the plasma sheath are studied. The ion flow in the sheath introduces an anisotropy, in particular "ion wakes" below the crystal particles. This leads to two types of transverse wave mode. It is shown that the "horizontal transverse mode" remains independent, but the "vertical transverse mode" and the longitudinal mode are coupled due to the particle-wake interaction. The coupling can drive an instability of the modes close to the point where their branches intersect. In addition, the particle-wake interaction might decrease the frequencies of the DL modes considerably.