Critical behavior of the fully frustrated q-state Potts piled-up-domino model

A q-state fully frustrated Potts model, the piled-up-domino model, is studied for different integer and noninteger values of q. Phase diagrams and some critical exponents are calculated using numerical transfer matrix methods. Foster, Gérard, and Puha [J. Phys. A 34, 5193 (2001)] have shown that there is a reentrant paramagnetic phase when q=3. It is shown here that the direction of reentrance changes as q passes through q=2 and disappears for a certain value of q=q*. The phase diagram of the model is radically different for q<q* and q>q*. Tentative numerical results suggest q*≈4.