Synchronized motion in two-dimensional complex plasma crystals

Kurzfassung

Two-dimensional complex plasma crystals are an ideal model system to study dynamic processes [1]. Recently, synchronized motion of alternating in-phase and anti-phase particle lines was observed during mode-coupling instability (MCI), where the out-of-plane mode couples to the longitudinal mode [2]. The coupling allows energy to be transferred from the flowing ions in the plasma sheath to the crystal until the crystal melts. While MCI is equally strong in three directions for an ideal hexagonal lattice [3], it was observed in only two directions in Ref. [2]. Here, we demonstrate with molecular dynamics simulations that an asymmetry in the horizontal confinement of the plasma crystal can cause an 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. Depending on the orientation of the confinement asymmetry, MCI and synchronized motion are observed in one or two directions. The good agreement of simulation and experiment suggests that the confinement asymmetry can be used to explain the synchronized motion observed in experiments. [1] Morfill G. E. and Ivlev A. V., Rev. Mod. Phys., 81 1353 (2009). [2] L. Couëdel, S. Zhdanov, V. Nosenko, A. V. Ivlev, H. M. Thomas, and G. E. Morfill, Phys. Rev. E 89, 053108 (2014). [3] S. K. Zhdanov, A. V. Ivlev, and G. Morfill, Phys. Plasmas 16, 083706 (2009).