Phase diagram of the restricted solid-on-solid model coupled to the Ising model

We study the phase transitions of a restricted solid-on-solid model coupled to an Ising model, which can be derived from the coupled XY-Ising model. There are two kinds of phase transition lines. One is a Ising transition line and the other is a surface-roughening transition line. The latter is a Kosterlitz-Thouless transition line from the viewpoint of the XY model. Using a microcanonical Monte Carlo technique, we obtain a very accurate two-dimensional phase diagram. The two transition lines are separate in the entire parameter space we study. This result is strong evidence that the fully frustrated XY model orders by two separate transitions and that roughening and reconstruction transitions of crystal surfaces occur separately.