Solid phases and pairing in a mixture of polar molecules and atoms

We consider a mixture of hard-core bosonic polar molecules, interacting via repulsive dipole-dipole interaction, and one atomic bosonic species. The mixture is confined on a two-dimensional square lattice and, at low enough temperatures, can be described by the two-component Bose-Hubbard model. The latter displays an extremely rich phase diagram including solid, superfluid, and supersolid phases. Here, we mainly focus on the checkerboard molecular solid, stabilized by the long-range dipolar interaction, and study how the presence of atoms affects its robustness both at zero and finite temperatures. We find that, due to atom-molecule interactions, solid phases can be stabilized at both (much) lower strengths of dipolar interaction and higher temperatures, than when no atoms are present. As a byproduct, atoms also order in a solid phase with the same melting temperatures as for molecules. Finally, we find that for large enough interaction between atoms and molecules, a paired supersolid phase can be stabilized. © 2011 American Physical Society.