Abstract
We present a detailed analysis of experimental study, which shows clear evidence of a two-stage melting process of a quasi-two-dimensional dusty plasma system in a high-frequency gas discharge. We accurately calculated global parameters of the orientational and translational order, as well as their susceptibilities to determine two critical points, related to “solid-to-hexatic” and “hexatic-to-liquid” phase transitions. The nature of the emerging defects and changes in their mutual concentration, in addition to the estimate of core energy of free dislocations also counts in favor of the formation of an intermediate hexatic phase. These results are fully consistent with the Berezinsky–Kosterlitz–Thouless theory.
Highlights
We present a detailed analysis of experimental study, which shows clear evidence of a two-stage melting process of a quasi-two-dimensional dusty plasma system in a high-frequency gas discharge
Y oung[9,10] and transformed eventually to Berezinsky–Kosterlitz–Thouless–Halperin–Nelson–Young (BKTHNY-) theory[11], which predicts two-step melting, from the crystal to liquid phase with formation of intermediate hexatic phase. It has short range translational and quasi-long-range orientational order, and phase transitions are caused by the creation and dissociation, binding and unbinding of topological defects, such as disclinations and dislocations
The authors concluded that the Grain-Boundary-Induced melting (GBI-)theory was best suited to a description of melting of two-dimensional dust structures, observed in their experiments
Summary
Metal-coated particles moved chaotically rather than uncoated ones as a response to external force At such conditions we observed an increase of particle kinetic energy without any evidence of any collective motions in a preferred direction, so that dusty plasma structure melted as a whole. (In our experiments it equaled ~ 5–10 min) Another advantage of our method is the ability to vary precisely the power of laser radiation and thereby change with a small step dust kinetic temperature without loss of heating uniformity so that we obtained a big set of experimental «points» with slightly varied dust parameters and still constant plasma parameters. Long time for establishing stationarity and homogeneity of the system during experiments together with original precision method of manipulating the kinetic temperature of dust particles allowed us to fulfill conditions needed to «catch» hexatic phase, never observed before in dusty plasmas
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