Abstract
Because of long-wavelength fluctuations, the nature of solids and phase transitions in 2D are different from those in 3D systems, and have been heavily debated in past decades, in which the focus was on the existence of hexatic phase. Here, by using large scale computer simulations, we investigate the melting transition in 2D systems of polydisperse hard disks. We find that, with increasing the particle size polydispersity, the melting transition can be qualitatively changed from the recently proposed two-stage process to the Kosterlitz-Thouless-Halperin-Nelson-Young scenario with significantly enlarged stability range for hexatic phase. Moreover, re-entrant melting transitions are found in high density systems of polydisperse hard disks, which were proven impossible in 3D polydisperse hard-sphere systems. These suggest a new fundamental difference between phase transitions in polydisperse systems in 2D and 3D.
Highlights
Because of long-wavelength fluctuations, the nature of solids and phase transitions in 2D are different from those in 3D systems, and have been heavily debated in past decades, in which the focus was on the existence of hexatic phase
By performing Monte Carlo (MC) simulations, we calculate the equation of state (EOS) for a system of 2562 =
By performing large scale computer simulations, we investigate the effect of particle size polydispersity on the phase behaviour of hard-disk systems
Summary
Because of long-wavelength fluctuations, the nature of solids and phase transitions in 2D are different from those in 3D systems, and have been heavily debated in past decades, in which the focus was on the existence of hexatic phase. With increasing the particle size polydispersity, the melting transition can be qualitatively changed from the recently proposed two-stage process to the KosterlitzThouless-Halperin-Nelson-Young scenario with significantly enlarged stability range for hexatic phase. Simulations of binary hard-disk mixtures showed that the presence of tiny amounts of small particles can eliminate the stability of hexatic phase[28] These highlight that the melting transition in 2D is subtle. We find that with increasing the polydispersity, the first-order hexatic-fluid transition becomes weaker, and completely switches to be continuous following the KTHNY scenario in PHDS with around 7% size polydispersity. In PHDS with slightly higher polydispersity, we observe re-entrant solid-hexatic and hexatic-fluid transitions at high density, which were proven impossible in 3D polydisperse hard-sphere systems[33]
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