MONTE-CARLO SIMULATION OF A COUPLED XY MODEL

Employing the Monte Carlo simulation technique, we have investigated s everal phase transitions exhibited by a coupled XY model in two dimens ions. The model is based on the Hamiltonian proposed by Bruinsma and A eppli [Phys. Rev. Lett. 48, 1625 (1982)]. The simulation results demon strate the existence of a new type of phase transition in which two di fferent orderings are simultaneously established through a continuous transition. The unique nature of this phase transition provides a plau sible explanation for our recent high-resolution heat-capacity data ne ar the smectic-A-hexatic-B transition of two-layer free-standing films .