Strong-weak coupling self-duality in the two-dimensional quantum phase transition of $p+ip$ superconducting arrays

The 2D quantum phase transition that occurs in a square lattice of $p+ip$ superconductors is used to show how four-body interactions in $d=2$ reproduce nonperturbative effects familiar from the study of two-body interactions in $d=1$. This model can be analyzed using an exact lattice self-duality of the associated 3D classical model; this duality is the 3D generalization of the Kramers-Wannier duality of the 2D Ising model, and there are similar exact dualities for certain many-spin interactions in dimensions $d\ge 3$. We also discuss the excitation spectrum in the ordered and disordered phases, and the relationship between our model and previously studied metallic behavior of boson models with four-boson interactions.