Equilibrium and Non‐Equilibrium Melting of Two‐Dimensional Plasma Crystals

Abstract

Recent progress in experimental and theoretical studies of melting of two‐dimensional (2D) plasma crystals is summarized. Several generic, equilibrium and non‐equilibrium processes which can be observed and investigated in 2D complex plasmas are discussed, such as KTHNY, grain‐boundary‐induced, and shear‐induced melting. Furthermore, the key features of the dominant plasma‐specific mechanism of melting operating in 2D plasma crystals, the mode‐coupling instability, are presented. The onset of the instability, which is characterized by threshold values of the experimental parameters, identifies the “dividing line” between the regimes when 2D complex plasmas can be employed to study generic strong‐coupling phenomena, and the situations when the melting occurs due to specific processes peculiar to complex plasmas. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mode couplings and resonance instabilities in finite dust chains

“…Figures 7(b)-7(d) show the dispersion relations obtained from the x, y, and z modes and correspond to the longitudinal, in-plane, and out-of-plane transverse DLWs, respectively. As shown, the in-plane transverse DLW exhibits optical wave characteristics and shows no coupling to other waves, in agreement with previous research [9,[23][24][25]45]. The longitudinal and out-of-plane transverse waves exhibit curved dispersion relations with rising and falling branches, similar to those observed experimentally and numerically for 2D [10][11][12][13][14]18,[23][24][25] and 1D [12,45] structures.…”

“…As shown, the in-plane transverse DLW exhibits optical wave characteristics and shows no coupling to other waves, in agreement with previous research [9,[23][24][25]45]. The longitudinal and out-of-plane transverse waves exhibit curved dispersion relations with rising and falling branches, similar to those observed experimentally and numerically for 2D [10][11][12][13][14]18,[23][24][25] and 1D [12,45] structures. In particular, the additional dispersion branches induced by coupling as observed in previous experiments [18,[23][24][25] can be clearly seen.…”

“…This is in excellent agreement with the case for large 2D crystals, where the in-plane transverse DLW shows no coupling to other waves [9,[23][24][25]. are not allowed.…”

“…Using a point charge model [8,9,[19][20][21][22] to simulate the ion wake, it has been shown that resonance instability can be triggered when the two coupled wave modes intersect. This phenomenon was recently observed experimentally [18,[23][24][25] in the thermal fluctuation spectrum illustrated by a high-energy-density region at the intersection between the DLWs. This enhanced energy density corresponds to the resonance instability and can result in melting of the plasma crystal at low neutral gas pressures [23][24][25][26].…”

“…This phenomenon was recently observed experimentally [18,[23][24][25] in the thermal fluctuation spectrum illustrated by a high-energy-density region at the intersection between the DLWs. This enhanced energy density corresponds to the resonance instability and can result in melting of the plasma crystal at low neutral gas pressures [23][24][25][26].…”