Mott-insulator-to-superconductor transition in a two-dimensional superlattice

We use quantum Monte Carlo and exact diagonalization calculations to study the Mott-insulator-to-superconductor quantum phase transition in a two-dimensional fermionic Hubbard model with attractive interactions in the presence of a superlattice potential. The model introduced offers unique possibilities to study such transitions in optical lattice experiments. We show that, in regimes with moderate to strong interactions, the transition belongs to the three-dimensional XY universality class. We also explore the character of the lowest-energy charge excitations in the insulating and superconducting phases and show that they can be fermionic or bosonic depending on the parameters chosen.