A couple examples of non-equilibrium melting and crystallization in 2D

Equilibrium 2D melting is among the most studied and best understood phase transitions. Hear we present experiments on nonequilibrium melting that mimics the conventional two stage melting controlled by the proliferation of dislocations and disclination. However, the topological defects are created by stirring rather than temperature and there is no effective temperature that maps the active system to its equilibrium counterpart. We also study melting in a Biased Random Organization model where overlapping particles are considered active and undergo a repulsive displacement δ, a “kick” 0<δ<𝜖, while non-overlapping particles are not moved. At low density the system evolves until there are no overlaps and motion stops – an absorbing phase. Above a critical density the system never finds a completely absorbing state and continues evolving forever. In 3D the system exhibits Random Close Packing at the absorbing/active boundary. In 2D the system is a close packed crystal with long range order at this boundary. This system melts with a first order transition as 𝜖 increases.