Perturbative density functional theory for phase transitions in a two-dimensional antiferromagnetic fluid

摘要

We study the temperature-density phase diagram of a fluid in two dimensions consisting of hard disks which, in addition, possess an internal (Ising) spin degree of freedom. The Ising spin of each disk couples with those of its neighbors via a short-ranged antiferromagnetic (AF) interaction. Recent Monte Carlo simulations have shown that this system undergoes a gas-liquid transition followed by a gas-AF-ordered-square-solid sublimation transition at low temperatures. Using a perturbative density functional approach we obtain, in addition to the observed transitions, a freezing transition at high density to a frustrated triangular solid phase. Interestingly, the calculated phase diagram suggests that at low temperatures, this transition is suppressed so that over a range of parameters, the system refuses to crystallize.