New Two-color Dimer Models with Critical Ground States

We define two new models on the square lattice, in which each allowed configuration is a superposition of a covering by ``white'' dimers and one by ``black'' dimers. Each model maps to a solid-on-solid (SOS) model in which the ``height'' field is two dimensional. Measuring the stiffness of the SOS fluctuations in the rough phase provides critical exponents of the dimer models. Using this ``height'' representation, we have performed Monte Carlo simulations. They confirm that each dimer model has critical correlations and belongs to a new universality class. In the "dimer-loop" model (which maps to a loop model) one height component is smooth but has unusual correlated fluctuations; the other height component is rough. In the ``noncrossing-dimer'' model, the heights are rough having two different elastic constants; an unusual form of its elastic theory implies anisotropic critical correlations.