Linear Conversion of Dust-Lattice Modes in Complex Plasmas

The linear coupling between transverse and longitudinal dus-lattice modes due to anisotropy in dust-dust interactions is considered. A character of DL mode interactions is determined by a sign of the coupling coefficient. When this term is negative, the DL waves remain stable, but demonstrate a specific mode conversion. In the opposite case of positive coupling coefficient, the dust-lattice waves can be subjected to a resonance instability, the criterion for which has been derived. This instability can explain experimentally observed spontaneous excitation of vibrational modes in a plasma crystal when the pressure is decreased below a critical value.