Anisotropy and synchronization during the mode-coupling instability

Abstract

Two-dimensional complex plasma crystals are an ideal model system to study dynamic processes on the kinetic level. Recently, synchronized motion of alternating in-phase and anti-phase particle lines was observed during the so-called mode-coupling instability (MCI), where the out-of-plane wave mode of the crystal couples to the longitudinal mode. While MCI is equally strong in three directions for an ideal hexagonal lattice, it was observed in only two directions in the experiment. Here, we demonstrate with molecular dynamics simulations that an asymmetry in the horizontal confinement of the plasma crystal can cause this anisotropic ignition of MCI. The confinement asymmetry leads to a deformation of the hexagonal lattice that is typically observed in experiments. The instability is accompanied by synchronized particle motion that is characterized by a new order parameter. This order parameter is sensitive to the explicit direction-dependency of the synchronization pattern.