Speaker
Description
The dependence of the mode-coupling instability threshold in two-dimensional complex plasma crystals is studied. It is shown that for a given microparticle suspension at a given discharge power there exist two thresholds in pressure. Above a specific pressure $p_\mathrm{max}$, the monolayer is always in the crystal phase. Below a specific pressure $p_\mathrm{min}$, the crystalline monolayer undergoes the mode-coupling instability and the monolayer is in the fluid phase. In between $p_\mathrm{in}$ and $p_\mathrm{max}$, the crystal will be in the fluid phase when increasing the pressure from below $p_\mathrm{min}$ until it reaches $p_\mathrm{max}$ where it recrystallises, while it remains in the crystal phase when decreasing the pressure from above $p_\mathrm{max}$ until it reaches $p_\mathrm{min}$. A simple auto-consistent sheath model can explain the melting threshold as a function of pressure and rf power due the changes of the sheath electric field and the microparticle charges leading to the crossing of the compressional in-plane phonon mode and the out-of plane phonon mode.
