Experimental observation of a first-order phase transition in a complex plasma monolayer crystal.

The formation and melting of a monolayered charged dust particle crystal in a DC glow discharge argon plasma is studied. The nature of the melting or formation process is established as a first-order phase transition from the variations in the Coulomb coupling parameter, the dust temperature, the structural order parameter, and from the existence of a hysteresis behavior. Our experimental results are distinctly different from existing theoretical predictions for two dimensional crystals based on the Kosterlitz-Thouless-Halperin-Nelson-Young mechanism or the grain boundary induced melting and indicate a mechanism that is akin to a fluctuation induced first-order phase transition in complex plasmas.