Full melting of a two-dimensional complex plasma crystal triggered by localized pulsed laser heating.

The full melting of a two-dimensional plasma crystal was induced in a principally stable monolayer by localized laser stimulation. Two distinct behaviors of the crystal after laser stimulation were observed depending on the amount of injected energy: (i) below a well-defined threshold, the laser melted area recrystallized; (ii) above the threshold, it expanded outwards in a similar fashion to mode-coupling instability-induced melting, rapidly destroying the crystalline order of the whole complex plasma monolayer. The reported experimental observations are due to the fluid mode-coupling instability, which can pump energy into the particle monolayer at a rate surpassing the heat transport and damping rates in the energetic localized melted spot, resulting in its further growth. This behavior exhibits remarkable similarities with impulsive spot heating in ordinary reactive matter.

Formation of bubbles, blobs, and surface cusps in complex plasmas.

Investigations of the dynamical evolution of a complex plasma, in which a vertical temperature gradient compensates gravity, were carried out. At low power the formation of microparticle bubbles, blobs, and spraying cusps was observed. This activity can be turned on and off by changing control parameters, such as the rf power and the gas pressure. Several observational effects indicate the presence of surface tension, even at small "nanoscales" of a few 100's of particles. By tracing the individual microparticle motion the detailed (atomistic) dynamics can be studied as well as the pressure dependence of the forces. A possible mechanism that could drive the observed phenomena is analogous to the Rayleigh-Taylor instability.

Dynamics of lane formation in driven binary complex plasmas.

The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane-formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems.

Highly resolved self-excited density waves in a complex plasma.

Experimental results on self-excited density waves in a complex plasma are presented. An argon plasma is produced in a capacitively coupled rf discharge at a low power and gas pressure. A cloud of microparticles is subjected to effective gravity in the range of 1-4 g by thermophoresis. The cloud is stretched horizontally (width/height approximately 45 mm/8 mm). The critical pressure for the onset of the waves increases with the temperature gradient. The waves are propagating in the direction of the ion drift. The wave frequency, phase velocity, and wavelength are measured, and particle migrations affected by the waves are analyzed at a time scale of 1 ms/frame and a subpixel space resolution.