8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

Wed 711:10-14:00P5.121Shear melting and shear flows in a 2D complex (dusty)plasmaVladimir Nosenko, 1 Alexei Ivlev, 1 and Gregor Morfill 11 Max-Planck Institute for extraterrestrial Physics, Giessenbachstra 1, 85741, Garching,GermanyA complex plasma is an ionized gas that has small particles of solid matter in it [1]. Micron-sizeparticles carry large negative charges. Due to their mutual interaction and external confinement,the particles can self-organize in structures that can have a crystalline or liquid order. Such orderedstructures are vastly softer than molecular materials and even colloidal crystals, so that they canbe easily manipulated, e. g. , by applying laser beams [2]. In contrast to colloidal dispersions, theparticle dynamics in plasma crystals is virtually undamped – the damping rate ν for individualparticles (caused by the friction on rarefied neutral gas) is weak, ν ≪ ω d . We studied theresponse of a monolayer complex plasma to a suddenly applied shear stress. A single layer ofdust particles was suspended in the sheath above the lower electrode in a capacitively-coupled rfdischarge in argon. The microspheres were made of Melamine Formaldehyde, had a diameterof 9.19 ± 0.09 µm, and acquired an electric charge of Q = −17 000 ± 1500e. The suspensionincluded ≈ 6000 particles and had a diameter of ≈ 60 mm. At our experimental conditions, theparticle suspension self-organized in a highly ordered triangular lattice. To apply a shear stressto the particle suspension, we used two counter-propagating laser beams. Beginning with anundisturbed lattice, we applied increasing levels of shear stress, and we observed that the particlesuspension passes through four stages: elastic deformation, defect generation while in a solidstate, onset of plastic flow, and fully developed shear flow. We discuss the stress threshold andanisotropy of shear-induced melting.[1] G. E. Morfill and A. V. Ivlev, Rev. Mod. Phys. 81, 1353 (2009).[2] V. Nosenko, S. K. Zhdanov, A. V. Ivlev, C. A. Knapek, and G. E. Morfill, Phys. Rev. Lett.103, 015001 (2009).121