Dedicated experiments on melting of 2D plasma crystals were carried out. The melting was always accompanied by spontaneous growth of the particle kinetic energy, suggesting a universal plasma-driven mechanism underlying the process. By measuring three principal dust-lattice (DL) wave modes simultaneously, it is unambiguously demonstrated that the melting occurs due to the resonance coupling between two of the DL modes. The variation of the wave modes with the experimental conditions, including the emergence of the resonant (hybrid) branch, reveals exceptionally good agreement with the theory of mode-coupling instability.PACS numbers: 52.27.Lw, 52.27.Gr Strongly coupled complex (dusty) plasmas play an important role in the existing hierarchy of soft matter states [1]. Along with complex fluids and granular media as prominent examples of "regular" soft matter, complex plasmas represent natural model systems which enable remarkably broad interdisciplinary research. The characteristic length-and timescales in such systems are dramatically stretched (e.g., in complex plasmas -to hundreds of microns and tens of milliseconds, respectively). Therefore, numerous generic processes occurring in classical fluids or solids can be studied in greatest detail, at the most fundamental "atomistic" level [1][2][3]. Especially important here are 2D systems, where the complete information about all particles can be obtained at each moment of time. The current experimental capabilities make 2D complex plasmas ideal for comprehensive experimental studies of the atomistic dynamics [1,2,4,5].The investigation of atomistic processes that trigger the melting and crystallization is of particular interest. It is well known that the mechanisms resulting in the destruction of the long-range crystalline order in 2D systems can be very different from those operating in 3D crystals: The classical Kosterlitz-Thouless-HalperinNelson-Young (KTHNY) theory of 2D melting [6] predicts two consecutive phase transitions (with an intermediate, so called "hexatic phase" in between). The alternative theory [7] relates 2D melting with the formation of dislocation chains ("grain boundaries") percolating the system. These are generic melting mechanisms which can operate in very different strongly coupled systems [8][9][10][11][12].When studying generic classical phenomena occurring in regular liquids and solids, the relevance of a model system (be it colloidal suspensions, granular media, or complex plasmas) becomes crucial. Of course, careful analysis is required in the context of a given phenomenon (or, class of phenomena), but one can certainly identify essential common principles. In particular, the applicability of the Hamiltonial approach for the analysis of atomistic dynamics (for instance, to investigate kinetics of phase transitions) is one of these basic principles. This implies that non-Hamiltonian (non-conservative) behavior peculiar to model systems should play minor role at the relevant timescales [13].Non-Hamiltonial behavior of particle ensembl...

Experiments with two-dimensional (2D) plasma crystals are usually carried out in rf plasma sheaths, where the interparticle interactions are modified due to the presence of plasma wakes. The wake-mediated interactions result in the coupling between wave modes in 2D crystals, which can trigger the mode-coupling instability and cause melting. The theory predicts a number of distinct fingerprints to be observed upon the instability onset, such as the emergence of a new hybrid mode, a critical angular dependence, a mixed polarization, and distinct thresholds. In this paper we summarize these key features and provide their detailed discussion, analyze the critical dependence on experimental parameters, and highlight the outstanding issues.

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